ensure example app works properly with backgrounding and interrupts

[hburgund]

RW apps need to behave like typical iOS audio apps, so we need to ensure that:

• the app can be backgrounded and the audio will continue to stream
• the user's location will continue to be updated so that the stream stays current even when backgrounded
• if phone call or other core feature interrupt happens, the audio fades out and the app sends a streams/:id/pause/ call to keep stream from updating while not in use
• post-interrupt, streams/:id/resume/ needs to be sent along with possibly other actions to interact properly with the default iOS behavior

I do not want us to do anything unexpected or weird wrt to user interactions and expectations, so using the default iOS behavior as much as possible will be great, but RW does have a few unique bits that need to be handled.