TopMenuBarCustomizer: Refactoring

* Moved "NavigationSites" handling to extension TopMenuBarCustomizer pt2
* Total Makeover for extension TopMenuBarCustomizer
* "NavigationSites" also support MW messages now
* Made some doc an cc

Change-Id: Id6cf25fd83d883170c727574d5858595befdf84d
Merge "TopMenuBarCustomizer: Refactoring"