Split IDialogNotifier from IDialogRenderable and make SfxViewShell
implement it.

We now just send the dialog UNO command to the backend and wait for core
to emit a 'created' dialog callback which signals dialog creation in the
backend. The client is then supposed to send the paint commands for
rendering the dialog.

Change-Id: I1bfbce83c17955fa0212408376d6bcd1b2d2d1dd