update all routes to use individual Spotify API objects about melrady

[seesjays]

Brought the auth scheme to spec.

There aren't many more, if any, backend changes to make now:

• Modularized everything instead of lumping every route and function into app.js like before.
• Cleaned up, optimized and commented a lot of my code
• Reduced authorization to middleware instead of its own route
• Moved some heavy calculations to the front end (dataManager.js)
• Restructured track objects and how they're created