Themes: Full support for AOSP Volume Panel

- Recreate VolumePanel with theme enegine UiContext.
- Revert this https://gerrit.paranoidandroid.co/#/c/4375/ since we don't have
  the code with the panel they refer to. Just leave UiContext commented out, maybe
  we'll need that lately.

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>
Change-Id: Ifc9fd02ec4d263050b7d5f689935fa5e82095d26