[SPARK-7298] Harmonize style of new visualizations

- Colors on the timeline now match the rest of the UI
- The expandable buttons to show timeline view, DAG, etc are now more visible
- Timeline text is smaller
- DAG visualization text and colors are more consistent throughout
- Fix some JavaScript style issues
- Various small fixes throughout (e.g. inconsistent capitalization, some confusing names, HTML escaping, etc)

Author: Matei Zaharia <matei@databricks.com>

Closes #5942 from mateiz/ui and squashes the following commits:

def38d0 [Matei Zaharia] Add some tooltips
4c5a364 [Matei Zaharia] Reduce stage and rank separation slightly
43dcbe3 [Matei Zaharia] Some updates to DAG
fac734a [Matei Zaharia] tweaks
6a6705d [Matei Zaharia] More fixes
67629f5 [Matei Zaharia] Various small tweaks