macOS hotplug support

[kerneljake]

macOS hotplug support

Handle runtime changes of default audio output device like pairing Bluetooth headphones, plugging/unplugging 3.5mm jack, changing Sound Output in Audio MIDI Setup, etc.

Tested on macOS 13.6 M1, 10.13.6 x86_64, 10.12.6 x86_64

Known issues:

• There can be a race condition after plugging in the 3.5mm jack but before the External Headphones device is available. Retrying the plug usually works.
• ZoomAudioDevice does not play nicely. It can be removed via CLI if you are not sharing programmatic audio.

[ralph-irving]

Merged. This is a great addition to squeezeplay for mac. Thanks again.