Change thread priority to improve response

Change-Id: I0512ad0d4b6e3beb86417b0d6af24c47b86a84f8
Specific action if DoubleTap on a known element
DoubleTap in empty space will zoom like before
DoubleTap on a known element will notify the app with the specific action message.

Change-Id: Ib6574dbe9254d0fc7278b947e2ff3b845d26b899