Update action bar style in app header UI.

- Update background color of actionbar
- Remove elevation of actionbar so it appears to be the same entity as
  app header.
- Add a shadow below app header view. We can't set elevation on app
  header unfortunately because that will add shadow all round the view,
  but we only want shadow below it.
- Updated app icon size/text size per to match UI spec.

Change-Id: I63d7fa42b859a008fa662aaf19848cd40529c2ff
Fix: 37207527
Fix: 37079248
Test: visual && make RunSettingsRoboTests