Random buisness logic.

playlist.js - represents a playlist made by a user.
track.js - represents an audio track
playmodeplaylist.js - an attempt at a fair playlist player, plays the playlist of the person with the longest time since their playlist was played.
playmodesechonest.js - all the different playmodes if echonest api is connected.
track.js - track model
user.js - user model