Chord progress

* Chord.id is now a property, not a function
* Better error handling in Chord class
* Renamed add_peer to addPeer in Chord for consistency
* When adding the first peer to a Chord instance, the joining procedure is
  started automatically.
* Chord.route(): When routing to an unknown peer, use the WebSocket
* ConnectionManager now adheres to the new Chord API and has no separate
  successCallback and errorCallback anymore but a single callback.