Clear callbacks of elm_gesture_layer when GestureRecognizer is deleted.
[Title] Clear callbacks of elm_gesture_layer when GestureRecognizer is deleted.
[Issue#] P130410-6692, P130411-4986, P130411-4980, P130412-5042
[Problem] The email application is crashed when we change the mail by flicking the view.
[Cause] The callback of elm_gesture_layer is called when ewk_view is deleted and deleted object is referenced by callback.
[Solution] Clear callbacks of elm_gesture_layer when GestureRecognizer is deleted.
Change-Id: I48fe55b39cc8914b24aeae1782cdcef3331535b6