Remove usage of MetaScreen
Remove any usage of MetaScreen, as it has been removed from libmutter in the API version 3. The corresponding functionality has been moved into three different places: MetaDisplay, MetaX11Display (for X11 specific functionality) and MetaWorkspaceManager.
https://bugzilla.gnome.org/show_bug.cgi?id=759538
This needs mutter!95 (merged)