This is the continuation of my BufferView/LyXView cleanup. This commit replaces Buffe...

This is the continuation of my BufferView/LyXView cleanup. This commit replaces BufferView->LyXView->getDialogs().[show(), update()] with BufferView signal emissions.
The associated WorkArea is then responsible to connect these signals to its LyXView parent.

* BufferView:
  - showDialog, showDialogWithData, showInsetDialog: new boost signals

* LyXView:
  - connectBufferView(), disconnectBufferView(): new method in charge of the connection/disconnection of the above signal to associate private methods (showDialog(), etc).

* WorkArea
  - setBufferView(): will connect/disconnect the BufferView to its LyXView parent.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@15068 a592a061-630c-0410-9148-cb99ea01b6c8