screen: change ScreenType to WindowType and add WindowReference typedef

src/sort_playlist.cpp

@@ -175,7 +175,7 @@ void SortPlaylistDialog::mouseButtonPressed(MEVENT me)
 				enterPressed();
 		}
 		else
-			Screen<ScreenType>::mouseButtonPressed(me);
+			Screen<WindowType>::mouseButtonPressed(me);
 	}
 }