[TASK] Removal of ObjectManager instance from DiscoveryService

All depending classes uses the ObjectManager or uses it through Extbase DIC (fx
the SignalSlot dispatcher for the BrushRegistry slot)
[TASK] Adding try...catch for BrushDiscovery configuration array processing
[FIX] Adding conditional rendering of the brushLoaderView rendering
[TASK] Adding ability to update serialized USER_INT pageRenderer instance for VHs
[TASK] Refactoring PageRenderer hooks into PageAsset Controller

The call to the PageRenderer render-preProcess hook comes to late if it comes to
page caching in conjunction with *_INT cObject usage.
[FIX] Removal of ::updatePageRendererForUncachedPageContext() from pageRenderer VHs
[FIX] Adding proper pageAssets plugin path to TS setup, adding Add.html template
[DOC] Adding documentation for page.1407710024 cObject
[TASK] Removing BrushLoader view in favor of PageAssets controller
[FIX] Removal of unused `use` statement (BrushLoaderView)
[FIX] Adding `plain` brush identifier - alias map entries
[FIX] Fixing LanguageSetting update class

Only brushes from current active Highlighter must be selected.
[FIX] Updating view tempalte for LanguageSetting update class
[FIX] Fixing typo in LanguageSetting update class view tempalte
[CLEANUP] Removal of cache entry