Refactor GuiApplication::getStatus().

Refactor GuiApplication::getStatus().

* I didn't like the fact that the heart of the dispatch/status machinery is in the default clause of a long switch statement. Now, it is clear that we enter the app in getStatus, which then asks the GuiApplication itself, the GuiView, the current BufferView, the current Buffer, the document BufferView, the document Buffer,

* Shouldn't we let BufferView call the Buffer getStatus() functions ?,

* This also makes sure that if a command is not handled, it is turned off. Before r34164 this was caused by the default clause in BufferView,

* Now it is prevented that if the document BufferView is the same as the current BufferView, that the getStatus() functions are called twice,

* A warning can be outputted if the LFUN is not handled.

PS I want to do the same for the dispatch function.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@34165 a592a061-630c-0410-9148-cb99ea01b6c8