Add Ganglia view for VisualEditor metrics

- contains two graphs: one for DOM retrieve events (broken down by cached /
  uncached / overall) and one for DOM save
- also removes TotalPageLoadTime from NavigationTiming view (not yet being
  populated with data).

Change-Id: I100c68c6fa4a0be2de723ef4d09e01e3e0b4cb57
Merge "Add Ganglia view for VisualEditor metrics" into production