Switch between headphone / speaker settings

[Tim Curtis]

We would need "Audio Device Profiles" to implement reliable I2S/USB interface switching.

The profile would specify something like below. Then MPD could be automatically configured when switching interfaces.

- Device Name (ex: Allo Boss DAC)
- Interface (I2S or USB)
- Volume control (Hardware, Software, None)
- Initial volume (0 - 100)

The existing Audio device DB could be used if "Volume control" and "Initial volume" columns were added but there would also need to be a maintenance screen for add/edit/delete Devices... Thats a bit of work.

-Tim