Update System UI to use theme colors.

Instead of using hardcoded values, use colorPrimary, colorAccent, etc
to style system UI. Required setting a theme on several views to
get the proper accent color in the right place.

Deletes a lot of hard-coded colors from the app.
Deletes an unused view: StatusBarHeaderView

BUG: 28625050
BUG: 29003410
BUG: 28625105
Change-Id: I46cd8eba7cf5afdab53c7882aa4aac5af46772a9