Observe AVAudioSessionRouteChangeNotification on iOS

[cerupcat]

On iOS, since iPhone 6s devices are locked to 48k sampleRates, yet headphone jacks can be 44.1k, it's important to listen to AVAudioSessionRouteChangeNotification (for route changes) and restart the audio if the sample rate changes. Otherwise, if you change sampleRates mid-way through and don't account for it, there will be weird audio sounds.

[danoli3]

Definitely needed!

Did you want to do the PR?

[cerupcat]

@danoli3 I'll see if I get a chance soon. For right now, I had to hack it in another way since there were a few issues I ran into trying to modify OF.