[Representation] Spec for DragGesture

Add spec for the drag gesture, as attached to a
representation of a domain object. WTD-521.

platform/representation/src/gestures/DragGesture.js

@@ -49,7 +49,7 @@ define(
             return {
                 destroy: function () {
                     // Detach listener
-                    element.attr('draggable', false);
+                    element.removeAttr('draggable');
                     element.off('dragstart', startDrag);
                 }
             };