QS Edit: Try to simplify drag logic

 - Don't forcibly move around items during dragging, instead let the
ItemTouchHelper handle where things can and cannot be dragged.
 - Try to trigger notify calls only when needed.
 - Tiles will sit in the first slot after being removed until the
   edit panel is closed.

Change-Id: I4780e64bc39292ed85e961ac089c69834245dfb4
Fixes: 28067638