Whenever a new media button receiver is registered, save it
in the settings.
When the system audio settings are reloaded or when the
AudioService is created, the registered media button receiver
is restored.
Whenever a package is removed from the system, remove
any media button receiver from the same package that are in
the media button receiver stack. If this causes the currently
registered receiver to change (i.e. the top of the stack),
this will cause an update of the receiver stored in the
system settings.
Note that unregistering a media button receiver will not
cause the receiver saved in the settings to be updated,
this is ON PURPOSE. This is to prevent well behaved
application who unregister their receiver at the destruction
of their service, to not receive the intent after a reboot,
and to not encourage applications to never unregister
their receiver.
Change-Id: I941b777debaa56e88de93c3b03aec40331ea9ab1
d589fea865