Refresh Devices

[adrum]

This solves the issue of refreshing the device list whenever it changes, including headphones being plugged in.

Pulls in SimplyCoreAudio, since it provides a list of functionality including event notifications and consistent ordering of devices when iterating.

SCA does require 10.12 or greater, so this also bump that requirement up a bit.

[adrum]

There will be a merge conflict after #9 is merged. I will resolve it after #9 is merged.

[tylerclark]

Any update on this? I have to quit the app after connecting to my AirPods every time and relaunch. This seems like it'll resolve it.