Cleaned up styles that has no effects and fixed some performance issues in timeline

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.