Restrict content types to certain templates as well as regions? #403

created_content_type(regions=...) feels too limited to me -- what if I have ten different templates each with a 'main' region, and I only want to allow ContentTypeX in the 'main' region of TemplateA? Am I missing something here? Currently this requires manually namespacing all registered regions like 'templatea-main', etc, but that gets messy and has a flow-on maintenance effect in calls to {% feincms_render... %} etc.

I suspect a syntax something like regions=('TemplateA.main', 'other', 'Contact.sidebar', 'OtherTemplate.') might work well -- this would allow the content in TemplateA's main region, regions keyed 'other' in *any template, Contact template's 'sidebar' region or any region within OtherTemplate. Alternatively we could introduce a templates kwarg, but I think the former is more flexible/powerful and nicely backward compatible.

This may also prompt a rethinking of the _feincms_all_regions internals to maintain a {template_key: regions} dictionary or similar instead.

Any thoughts/suggestions? I may embark upon this shortly...