Add websocket server and basic song abstractions

[ianks]

Main thing here is the ability to connect to a websocket for real-time data about incoming traffic. We will eventually just have this data come from an Arduino sensor as people walk in through the Atlas building.

You will also be able to represent songs using JSON notation à là:

var jingleBells = {
  name: "Jingle Bells",
  notes: _.map([
    "E","E","E","E","E","E","E","G","C","D","E",
    "F","F","F","F","F","E","E","E","E","E","D","D","E","D",
    "E","E","E","E","E","E","E","G","C","D","E",
    "F","F","F","F","F","E","E","E","E","G","G","F","D","C"
    ], function(n) { return notesMap[n]; })
};

[ianks]

cc: @atlastrafficmonitor/owners