Clear rogue references (playcanvas#1431)

* Clear material value in mesh instances when removing them so material doesn't maintain reference to unused meshinstance

* Remove visible lists when cameras are removed from layers

* Remove event listeners in destroy for sound component, camera component, particle component, model component

* [FIX] layoutgroup system now reflows in correct order

In ElementInput don't make touchcancel listener passive

Merge branch 'master' into stable

Update only shaders that depends on lighting on COMPUPDATED_LIGHTS (p…

…laycanvas#1421)

Prevent initialize() overwriting textures to null if they are waiting…

… on an asset to be loaded (playcanvas#1406)

initialize() is called on a material immediately after the placeholder textures are assigned. The source data currently replaces asset id with the actual texture and initialize would clear to null if the data didn't contain the texture. Instead we now also check if it is an asset id, in which case we can wait until the asset is loaded and leave the placeholder texture.

This prevents additional shader compilation calls (because the number of textures on the material changes).

[FIX] Remove uses of pc.Vec2/4#data for light cookies. (playcanvas#1405)

Merge pull request playcanvas#1402 from playcanvas/elementinput-options

pc.ElementInput useMouse and useTouch

Fix VAO PR.

Merge branch 'master' of ssh://github.com/playcanvas/engine

Prevent error when spriteAsset is changed before texture atlas load h…

…as completed (playcanvas#1381)