* Use factored audio code from AudioLayer
* Properly refresh device list on device change
* After device change, use preferred device if possible

PulseAudio device selection was broken because only
a single device can use echo cancelling at a time,
so when the second device was opened, the first echo-canc3elled stream
was redirected to it.

Use per-stream instead of per-context echo-cancellation.
Only use echo-cancellation for playback and record (disabled for ringtone).

Tuleap: #207
Change-Id: Ib5fcb3795a079a867e44c743892bb1325d0f4eef