The BufferView/WorkArea/LyXView reorg a.k.a Multiple WorkAreas:

The BufferView/WorkArea/LyXView reorg a.k.a Multiple WorkAreas:

* Buffer:
- get rid of cursor_ and anchor_
- ~Buffer(): update the labels of its master buffer before closing
- closing(): pass the Buffer address.

* BufferView():
- BufferView(): needs a valid Buffer (should be const in the future.
- most of the change is about removing all test of buffer_ nullity.
- resize(): deleted.
- setBuffer(): deleted.

* Application:
- newLyXView(): simplification
- updated design description in Application.h

* Gui/GuiImplementation: remove all WorkAreas and BufferView creation/Deletion. Workareas are directly handled by  LyXView/GuiView and BufferView is created/delete by WorkArea.

* LyXView/GuiView: implement the new design

What is not working yet:
- the close tab button: it is implemented but does not show up.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@19686 a592a061-630c-0410-9148-cb99ea01b6c8