Help reduce falsing on the seek bar

To help reduce falsing, only accepting two gestures:
 - single tap anywhere to seek to that position
 - scroll starting from the thumb
All other guestures will be handled by the carousel.

Bug: 155673905
Test: manual - play music and tap anywhere. Verify that playback
position changes.
Test: manual - play music and drag thumb. Verify that playback position
changes.
Test: manual - play music and drag on seek bar away from thumb. Verify
that playback position doesn't change.

Change-Id: I11f93de5e61a679c9d56ca98b478e793d73daa13