Add "Dummy Output" detection
Submitted by Bastien Nocera
We should make it possible and easy to detect whether the machine on which we're running doesn't have any sound output, or sound input, so we could hide the output or input tabs, as necessary, in the Sound Settings.
This would also allow us to hide the volume bar and volume icon in the system status area, which would be more useful than changing the volume on a non-existent device.
Version: git master