Enable doctrine database connection. - #17

Description
-----------

Currently Contao 4.6 implicitly requires at least Symfony 4.1, because we need `symfony/http-kernel` and `symfony/monolog-bridge` in at least version 4.1.

However, if we stop requiring `symfony/symfony`, all components but the two mentioned above could be installed in version 3.4, 4.0 or 4.1, therefore this PR replaces requirements for `symfony/symfony` and for `symfony/framework-bundle` with their respective components.

@contao/developers Do you prefer merging this PR so Contao 4.6 is compatible with Symfony 3.4 or do you prefer to keep `symfony/symfony` with Contao 4.6 not being compatible with Symfony <4.1 anymore?

Commits
-------

d5bcc375 No longer require symfony/symfony and symfony/framework-bundle
0270c5dc Remove support for Symfony 4.0
57303ac0 Remove an unused dependency

Description
-----------

With @Toflar we have discovered by accident that if a URL is double-encoded (for some reason, doesn't matter) the Contao's `RouteProvider` will eventually throw an error trying to query a database.

```
URL original: drachenlochmuseum-v%25c3%25a4ttis.html
URL decoded: drachenlochmuseum-v%c3%a4ttis.html
URL decoded 2nd time: drachenlochmuseum-vättis.html
```

The decoded URL is used in the database query and that fails because the database driver would like to replace wildcards `%c` with parameters that were not provided.

Stack trace:

```
Exception: Too few arguments to build the query string
#27 vendor/contao/core-bundle/src/Resources/contao/library/Contao/Database/Statement.php(304): replaceWildcards
#26 vendor/contao/core-bundle/src/Resources/contao/library/Contao/Database/Statement.php(249): execute
#25 vendor/contao/core-bundle/src/Resources/contao/library/Contao/Model.php(1102): find
#24 vendor/contao/core-bundle/src/Resources/contao/library/Contao/Model.php(973): findBy
#23 vendor/contao/core-bundle/src/Framework/Adapter.php(38): __call
#22 vendor/contao/core-bundle/src/Routing/RouteProvider.php(493): findPages
#21 vendor/contao/core-bundle/src/Routing/RouteProvider.php(88): getRouteCollectionForRequest
#20 vendor/contao/core-bundle/src/Routing/LegacyRouteProvider.php(43): getRouteCollectionForRequest
#19 vendor/symfony-cmf/routing/src/NestedMatcher/NestedMatcher.php(141): matchRequest
#18 vendor/contao/core-bundle/src/Routing/Matcher/LegacyMatcher.php(69): matchRequest
#17 vendor/symfony-cmf/routing/src/DynamicRouter.php(271): matchRequest
#16 vendor/symfony-cmf/routing/src/ChainRouter.php(188): doMatch
#15 vendor/symfony-cmf/routing/src/ChainRouter.php(158): matchRequest
#14 vendor/symfony/http-kernel/EventListener/RouterListener.php(115): onKernelRequest
#13 vendor/symfony/event-dispatcher/EventDispatcher.php(212): doDispatch
#12 vendor/symfony/event-dispatcher/EventDispatcher.php(44): dispatch
#11 vendor/symfony/http-kernel/HttpKernel.php(126): handleRaw
#10 vendor/symfony/http-kernel/HttpKernel.php(67): handle
#9 vendor/symfony/http-kernel/Kernel.php(198): handle
#8 vendor/symfony/http-kernel/HttpCache/SubRequestHandler.php(85): handle
#7 vendor/symfony/http-kernel/HttpCache/HttpCache.php(448): forward
#6 vendor/symfony/framework-bundle/HttpCache/HttpCache.php(57): forward
#5 vendor/symfony/http-kernel/HttpCache/HttpCache.php(420): fetch
#4 vendor/contao/manager-bundle/src/HttpKernel/ContaoCache.php(46): fetch
#3 vendor/symfony/http-kernel/HttpCache/HttpCache.php(317): lookup
#2 vendor/symfony/http-kernel/HttpCache/HttpCache.php(192): handle
#1 vendor/friendsofsymfony/http-cache/src/SymfonyCache/EventDispatchingHttpCache.php(98): handle
#0 web/app.php(58): null
```

Commits
-------

8ae25820 Fix a potential error if the URL has percentage in it
8caaf252 Fix unit tests
509f7624 Correctly encode the page aliases

… #7248)

Description
-----------

If a `tl_article` record still contains `keywords` from previous Contao versions and you reference this article in an `article` content element, the following warning will appear in the back end:

```
ErrorException: Warning: Undefined global variable $TL_KEYWORDS
#24 /vendor/contao/core-bundle/src/Resources/contao/modules/ModuleArticle.php(207): Contao\ModuleArticle::compile
#23 /vendor/contao/core-bundle/src/Resources/contao/modules/Module.php(214): Contao\Module::generate
#22 /vendor/contao/core-bundle/src/Resources/contao/modules/ModuleArticle.php(70): Contao\ModuleArticle::generate
#21 /vendor/contao/core-bundle/src/Resources/contao/library/Contao/Controller.php(550): Contao\Controller::getArticle
#20 /vendor/contao/core-bundle/src/Resources/contao/elements/ContentArticle.php(30): Contao\ContentArticle::generate
#19 /vendor/contao/core-bundle/src/Resources/contao/library/Contao/Controller.php(622): Contao\Controller::getContentElement
#18 /var/cache/prod/contao/dca/tl_content.php(318): tl_content::addCteType
#17 /vendor/contao/core-bundle/src/Resources/contao/drivers/DC_Table.php(4717): Contao\DC_Table::parentView
#16 /vendor/contao/core-bundle/src/Resources/contao/drivers/DC_Table.php(313): Contao\DC_Table::showAll
#15 /vendor/contao/core-bundle/src/Resources/contao/classes/Backend.php(667): Contao\Backend::getBackendModule
#14 /vendor/contao/core-bundle/src/Resources/contao/controllers/BackendMain.php(168): Contao\BackendMain::run
#13 /vendor/contao/core-bundle/src/Controller/BackendController.php(49): Contao\CoreBundle\Controller\BackendController::mainAction
#12 /vendor/symfony/http-kernel/HttpKernel.php(163): Symfony\Component\HttpKernel\HttpKernel::handleRaw
#11 /vendor/symfony/http-kernel/HttpKernel.php(75): Symfony\Component\HttpKernel\HttpKernel::handle
#10 /vendor/symfony/http-kernel/Kernel.php(202): Symfony\Component\HttpKernel\Kernel::handle
#9 /vendor/symfony/http-kernel/HttpCache/SubRequestHandler.php(86): Symfony\Component\HttpKernel\HttpCache\SubRequestHandler::handle
#8 /vendor/symfony/http-kernel/HttpCache/HttpCache.php(481): Symfony\Component\HttpKernel\HttpCache\HttpCache::forward
#7 /vendor/symfony/framework-bundle/HttpCache/HttpCache.php(73): Symfony\Bundle\FrameworkBundle\HttpCache\HttpCache::forward
#6 /vendor/symfony/http-kernel/HttpCache/HttpCache.php(454): Symfony\Component\HttpKernel\HttpCache\HttpCache::fetch
#5 /vendor/contao/manager-bundle/src/HttpKernel/ContaoCache.php(66): Contao\ManagerBundle\HttpKernel\ContaoCache::fetch
#4 /vendor/symfony/http-kernel/HttpCache/HttpCache.php(348): Symfony\Component\HttpKernel\HttpCache\HttpCache::lookup
#3 /vendor/symfony/http-kernel/HttpCache/HttpCache.php(226): Symfony\Component\HttpKernel\HttpCache\HttpCache::handle
#2 /vendor/friendsofsymfony/http-cache/src/SymfonyCache/EventDispatchingHttpCache.php(96): Contao\ManagerBundle\HttpKernel\ContaoCache::handle
#1 /web/index.php(44): require
#0 /web/app.php(13): null
```

This is because `$GLOBALS['TL_KEYWORDS']` is only initialised in the front end within `PageRegular::prepare()`. This PR simply ignores it if not set.

Commits
-------

e54dc2b8 fix warning when legacy keywords are present

…#7268)

Description
-----------

Got this erro in my logs:

```
RuntimeException: The Symfony container is not available, did you initialize the Contao framework? in vendor/contao/core-bundle/contao/library/Contao/System.php:143 Stack trace:
#0 vendor/contao/core-bundle/contao/library/Contao/System.php(97): Contao\System->import('Contao\\Config', 'Config')
#1 vendor/contao/core-bundle/contao/library/Contao/DcaExtractor.php(105): Contao\System->__construct()
#2 vendor/contao/core-bundle/contao/library/Contao/DcaExtractor.php(140): Contao\DcaExtractor->__construct('tl_opt_in')
#3 vendor/contao/core-bundle/contao/library/Contao/Model.php(291): Contao\DcaExtractor::getInstance('tl_opt_in')
#4 vendor/contao/core-bundle/contao/library/Contao/Model.php(1084): Contao\Model::getUniqueFields()
#5 vendor/contao/core-bundle/contao/models/OptInModel.php(87): Contao\Model::findBy(Array, 1716888783, Array)
#6 vendor/contao/core-bundle/src/Framework/Adapter.php(38): Contao\OptInModel::findExpiredTokens()
#7 vendor/contao/core-bundle/src/OptIn/OptIn.php(76): Contao\CoreBundle\Framework\Adapter->__call('findExpiredToke...', Array)
#8 vendor/contao/core-bundle/src/Cron/PurgeOptInTokensCron.php(30): Contao\CoreBundle\OptIn\OptIn->purgeTokens()
#9 vendor/contao/core-bundle/src/Cron/CronJob.php(44): Contao\CoreBundle\Cron\PurgeOptInTokensCron->__invoke('cli')
#10 vendor/contao/core-bundle/src/Cron/Cron.php(197): Contao\CoreBundle\Cron\CronJob->__invoke('cli')
#11 vendor/contao/core-bundle/src/Cron/Cron.php(182): Contao\CoreBundle\Cron\Cron->executeCrons(Array, 'cli', Object(Closure))
#12 vendor/contao/core-bundle/src/Cron/Cron.php(97): Contao\CoreBundle\Cron\Cron->doRun(Array, 'cli', false)
#13 vendor/contao/core-bundle/src/Command/CronCommand.php(53): Contao\CoreBundle\Cron\Cron->run('cli', false)
#14 vendor/symfony/console/Command/Command.php(326): Contao\CoreBundle\Command\CronCommand->execute(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#15 vendor/symfony/console/Application.php(1096): Symfony\Component\Console\Command\Command->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#16 vendor/symfony/framework-bundle/Console/Application.php(126): Symfony\Component\Console\Application->doRunCommand(Object(Contao\CoreBundle\Command\CronCommand), Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#17 vendor/symfony/console/Application.php(324): Symfony\Bundle\FrameworkBundle\Console\Application->doRunCommand(Object(Contao\CoreBundle\Command\CronCommand), Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#18 vendor/symfony/framework-bundle/Console/Application.php(80): Symfony\Component\Console\Application->doRun(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#19 vendor/symfony/console/Application.php(175): Symfony\Bundle\FrameworkBundle\Console\Application->doRun(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#20 vendor/contao/manager-bundle/bin/contao-console(40): Symfony\Component\Console\Application->run(Object(Symfony\Component\Console\Input\ArgvInput))
#21 vendor/bin/contao-console(119):  #22
```

Commits
-------

9ee76a07 Initialize the Contao framework when working with opt-in tokens