The DataChannel Polyfill for older browsers

Added the RTCDataChannel object for older browsers using the [DataChannel Polyfill](https://github.com/piranna/DataChannel-polyfill/blob/master/datachannel.js) fallback by Jesús Leganés Combarro, built on top of WebSockets.

This is just a proof of concept and it should be thoroughly tested and tailored to your needs.

It would be really nice to get PeerJS working in current browsers, not only Chrome Canary.