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
Sure, there are different patterns to expose functions of a class. This one in particular is the 'Revealing Pattern.' The return provides an interface for the functions of the object. It's my go to pattern when I want to create an object that is instantiated at runtime and has only once instance of itself. This book is great for finding the right pattern for the job: http://addyosmani.com/resources/essentialjsdesignpatterns/book/#revealingmodulepatternjavascript