Support arbitrary stations

[holman]

I want to stash the concept of stations in Play. We have multiple DJs that we livestream at GitHub, and we want to eventually show the entire listing of currently-playing DJs next to the main Play stream in play/play-cocoa.

I'm not sure how this will work yet, but most likely it'll mean we'll add our private DJ domain to play.yml and then we include that listing in an API endpoint to clients. I suspect the domain will be an aggregate feed, so a URL like:

/streams.json

Will actually be a listing of multiple stream URLs. Schema TBD.