* Now ModestWindowMgr, methods close_all_windows and register_window now

* Now ModestWindowMgr, methods close_all_windows and register_window now
  return a boolean to know if we really did the operation. We can fail
  for example on the cases where a dialog is blocking a window to be
  closed.
* Now we use those booleans to check error conditions, mainly for
  hildon2 window management policies.
* Now we show mandatory the save to drafts information banner, and
  without a parent (then it's not tied to
* New hildon2 implementation for window manager, heavily based on
  stackable windows behavior. This implements the ui specs policy for
  dialogs (close windows unless dialogs are open, then present).
* This policy doesn't provide fullscreen nor toolbar settings.

pmo-trunk-r6045