Swipe down on hotseat to launch recent task

If you're ever in overview and swipe down on the hotseat, it will launch
the focused task *unless* you entered overview from the workspace and
have not scrolled past the first task. This is a hidden state to allow
for reversibility of the swipe up from workspace.

Also moved PendingAnimation from quickstep to launcher3.

Change-Id: Iea077bc0ef7c74f6bf7b98d0a638892b9c5fe36c