Reimplement UI without any indication of percentage or mutedness,
and whitout switches. The only interaction point is slider, but
it still supports mute changing for applications that track it,
and will react appropriately to external changes.
https://bugzilla.gnome.org/show_bug.cgi?id=634329
_volumeChanged should not update the icon if the sink is muted.
Fixes the case when shell is started with a muted sink (_mutedChanged
is called before _volumeChanged).
https://bugzilla.gnome.org/show_bug.cgi?id=632868
Add volume control indicator which uses API from gnome-volume-control
to interact with PulseAudio and shows both input and output volumes.
Also adds a small wrapper around libcanberra in ShellGlobal, used by the
volume indicator to provide auditive feedback.
https://bugzilla.gnome.org/show_bug.cgi?id=629455