BGMApp now disables BGMDevice's volume and/or mute controls if the
output device selected in BGMApp doesn't have matching controls. This
prevents the controls from being presented to the user when they don't
do anything.
In BGMPlayThrough, wait much longer for our IOProcs to stop themselves
before assuming something's gone wrong. In testing, rapidly changing
between output devices with and without controls while playing audio
would occasionally cause one of the IOProcs to take too long to stop
itself.
Also adds some basic scriptability, mainly so UI tests can use
AppleScript to check BGMApp's state that would be complicated to check
otherwise. (In this case, to check which output device is selected.)
Fixes#101.
We only unpause the music player, after auto-pausing it, if it's been
paused for longer than some minimum length of time. This commit reduces
that time if the music player hasn't been paused for long.
