Volume: Improve inline volume controls used in settings.

 - Make the system internal ringer mode change signal available to
   other system components via a standard intent, instead of a
   volume-controller-only binder call.
 - Update sysui to use new intent for icon policy.
 - Add proper muting state to the volumizer, to look more like
   the associated volume panel slider.
 - Add basic ringer mode state tracking for the notification-ring
   slider setting.

Bug: 17899613
Change-Id: Ie2df52edb070055ef59c74039162a0e785d2fdbb