Fixing issue where you couldn't drag an item multiple pages (issue 10754544)

-> This was caused by a strange race condition. The page snap time was equal to
   the delay to recheck whether to snap (in DragController). This meant that
   scrollRight()/Left() would get called, and the scroller would be finished
   however, the final computeScrollHelper() hadn't been called, so the mCurrentPage
   hadn't yet been incremented.
-> Fixed the underlying race condition.
-> Added suitable gap (150 ms) between the two delays.

Change-Id: If700eb9e14d77a174e4395ca6933119bdb0da768