* Add new Trait tUIContentAreas to handle multiple content areas across UIBlock classes (extracted from PageContent)
* Remove return type hinting in some method when type was "self" or the class itself when it's meant to be overloaded (works only with PHP 7.4+)
* Update some PHPDoc
* Reformat some brackets
- iTopWebPage: Restore "open search" feature
- iTopWebPage: Change all resources URL to absolute in order to benefit from the "duplicate removal" benefits
- iTopWebPage: Remove obsolete method IsMenuPaneVisible()
- Config: Add new parameters quick_create.enabled / global_search.enabled / breadcrumb.enabled
- utils: Add new GetAppRevisionNumber() method
- Introduce iUIBlock interface for UI layouts, components, ...
- Introduce BlockRenderer to properly render blocks
- Add "render_block" function to TwigHelper to render blocks directly from TWIG
- Refactor layouts and components into proper block classes to fit the new architecture