Add overscroll to the top of All Apps.

* Overscroll at the top of all apps will occur when the user scrolls
  up, hits the top, and continues to scroll up.
* Fixed bug where All Apps jumps when the user enters overscroll
  from a scroll that doesn't start at the bottom.
* Fix bug where AllAppsRecyclerView stays translated even after
  the user has finished dragging.

Bug: 62628421
Change-Id: Ia1d230a7cc07a7cf8c1a7c5211a025034ae5f6df