Add a wrapper around tweener to do some extra integration

Automatically removes tweens on destroyed actors, and provides
additional "animation started/stopped" callbacks (eg, for tracking
whether or not to show window clone titles)

js/ui/windowManager.js

@@ -4,9 +4,9 @@ const Clutter = imports.gi.Clutter;
 const Mainloop = imports.mainloop;
 const Meta = imports.gi.Meta;
 const Shell = imports.gi.Shell;
-const Tweener = imports.tweener.tweener;
 
 const Main = imports.ui.main;
+const Tweener = imports.ui.tweener;
 
 const WINDOW_ANIMATION_TIME = 0.25;
 const SWITCH_ANIMATION_TIME = 0.5;