Use FlingAnimationUtils for dismissing a notification

Addressing comment in ag/877913 PS6

Adds FlingAnimationUtils to SwipeHelper for dismissing notification
so that it may better follow a user's finger. This is not used
when a dismiss all is called (i.e. useAcceleration is requested).

Additionally alters dismiss behavior to accelerate out if velocity
was 0.

Change-Id: Ia7dc15d64e8427d5cfbdee3f4e48ccd60f5b0b36