Audio Devices only detected at startup

[srcejon]

The list of audio devices appears to only be detected at start-up, so SDRangel doesn't recognize when an audio device is connected or removed, while running.

While connection of most audio devices is probably fairly infrequent (E.g. HDMI/USB), so not much of a problem, the particular use-case I'm interested in is when using a Remote Desktop Connection. The audio devices can change in order to allow audio to be re-directed to the RDP client, and it would be nice not to have to restart SDRangel to get audio.