First working Chord version (using successor lists)

* Added error handling in joining procedure
* Chord.join() can now only be called once per instance
* Signaling messages are now always routed through the bootstrap server so that
  we don't end up calling Chord.route() in a loop
* Fixed typo in Node.successor()
* ConnectionManager improvements:
  * It is now possible to open multiple connections to a remote peer. For this
    to work, every signaling message now carries a unique sequence number
  * Improved error handling
Fixed mesh router

* The callback gets an error as first parameter