Modifications to allow notification header to be customized.

Changes include:
- Allowing the margins between header items to be customized.
- Allow expand button to be laid out at the end of the header view.
- Ensure the media header height can be customized.
- Allow entire header to be clicked to expand the notification rather
than just the notification button.

Also, fix how the color is resolved from the header. It currently checks
the color directly on the expand button. However, this color can simply
be retrieved by the header's getOriginalNotificationColor() method.

Test: booted on phone and Android Auto headunit
Bug: 33210494
Change-Id: I4bb3ff42d23b44de28dc1196799a7c3bda40bbac