Serves coffeeshop audio from s3 url in production.

Consistently serving a media file slowed some realtime messaging calls.
The fix was to serve media files from s3 instead of from the rails app
itself.

* Other envs still play local file at public/audio/coffee.mp3
  * Much easier to test!
* Reduces mp3 file size to 50% of original.
  * (reduced bitrate to 128kbps)