[DND] Use Params for DND.makeDraggable()

Replace boolean 'manualMode' with a params object for
improved readability and future expansion.

https://bugzilla.gnome.org/show_bug.cgi?id=613367

js/ui/appDisplay.js

@@ -404,7 +404,8 @@ AppWellIcon.prototype = {
         this.actor.connect('clicked', Lang.bind(this, this._onClicked));
         this._menu = null;
 
-        this._draggable = DND.makeDraggable(this.actor, true);
+        this._draggable = DND.makeDraggable(this.actor,
+                                            { manualMode: true });
         this._dragStartX = null;
         this._dragStartY = null;