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
I'm interested in this way of you define this class (sub class?). I'm pretty new to Javascript and I've been struggling to get a class that can initialize itself. This solution works, (which is more than I've been able to achieve!) but I wish I could just look at the function names to know how to call the methods. Is there a way to define a pattern class that does not have this translation layer?