Allow swipe down to dismiss for ResolverDrawerLayout

Let the user swipe the intent resolver UI off of the screen to get rid
of it. So satisfying!

Also fix a bug where transitioning between touching the area outside
of the drawer to the drawer itself would misbehave or otherwise
dismiss when it shouldn't.

Bug 18026675

Change-Id: I456cc22b9575dc4c65e45154dc81201fe2045adc