timeline updates

1. get rid of the css that don't have any effect on the style
2. fixed some performance issues:
      - binding to clientWidth and clientHeight will trigger the observer callback a lot of times
      - onPlayerTimeChanged in wat-timeline-scrubber changes playertime which causes the function itself get call again.
3. enable touch events on timeline-scrubber.
4. stop highlighting the animation that is playing because it is not really helpful to the user.