Issue #29 Pressing play while playing should restart the current track

- If already playing, use existing stop.
- Included underscore.js in project to make searching arrays easier. Can refactor to vanilla JS w/o library

Cheers
Yes, indeed. You'll see that in the init, I have a _mediaPlayer variable. That was the next step to take all of the instances of "self.media" and make them "_mediaPlayer" types.