[AppWell] Allow popup menu to be persistent, and support direct window selection

When the user click+hold+release over the icon, the effect we want
is for the menu to stick around.

Also, allow the user to mouse over the actual windows and select
them directly.  If the user mouses over a window, reflect that in
the menu.

js/ui/overview.js

@@ -371,6 +371,17 @@ Overview.prototype = {
             this.show();
     },
 
+    /**
+     * lookupCloneForWindow:
+     * @metaWindow: A #MetaWindow
+     *
+     * Given a #MetaWindow instance, find the WindowClone object
+     * which represents it in the workspaces display.
+     */
+    lookupCloneForWindow: function (metaWindow) {
+        return this._workspaces.lookupCloneForMetaWindow(metaWindow);
+    },
+
     /**
      * activateWindow:
      * @metaWindow: A #MetaWindow