QS: Add long-press to customize prototype - part 2

 - Add info/remove drop targets that appear during dragging
 - Move drag start into NonPagedTileLayout so that both start
   and end of tile move drags are in the same place.
 - Still needs way to add tiles

Change-Id: If843ebbb86f393b461289c1407c6a82b6a5aed9d