Add an extensible Message Processing system for sub-protocol extensions.

* Adds a generic processor pool that extensions can hook into to add
  custom message routing or processing logic based on the message type.
* Exposes an API for message processors to give them access to utilities
  such as the event router, channel manager, and synchronization system.
* Changes the current Dispatcher class into a generic message queue
  manaager.
* Moves the current WebsocketRails message processing into a default
  EventProcessor class that utilizes the new Processor API.

Update the Default JavaScript client to match the new server changes.
Fix channel tokens in the JavaScript client.
Remove debugging output from the Connection class.