Delegate horizontal scrolls from the Hotseat to the Workspace

=> Before this change, scrolling horizontally on the the hotseat area was a no-op
=> This is a mild usability issue (or arguably WAI) for the default grid, but for larger grids it feels really broken as you have to reach very high just to scroll to another page.

issue 156507399

Test: manual. Also verified that swipe up still works and goes through the same code path.

Change-Id: I760aca473dd36bc8cfb906cb58e897e2ab7fd1d9