Volume: new coat of paint.

- Two sections (lighter header, darker detail) like QS.
- Fewer text variants.
- Remove backgrounds for segmented buttons.
- Remove alarm warning background.
- Fix slider-only style.
- Ensure all touch-targets are 48dp.

Bug:16419191

Change-Id: I220f3a736eba3dd7a1b9ff58a8fe4bf3d21db61a