Add 'type' field to central Event class, allow handlers to match

Now in addition to specific events, omega clients will be able
to subcribe to custom groupings of events as dispatched by a
running server
Switch user event tracking to be based on type and not id

Resolves a FIXME where we needed to generate unique id's for
the registered_user event. Now that events can be subscribed
to by type clients can subscribe to whole classes of user
(or any other) events

Specs updated to match new functionality