Add paper to dashboard upon collaboration changes

References:
* https://www.pivotaltracker.com/story/show/77045390

Major changes:
* event stream now contains a user stream that can listen for specific events for a specific user
* generalizes event stream destroy action to work for any model (not just task)
* adds ability to refresh a user's event channels

--- AC + CT

OK, upon digging deeper, I learned that this object is passed on to [`EventStream.stream_names`](https://github.com/Tahi-project/tahi/blob/new-paper-subscriptions/app/services/event_stream.rb#L21-L29) which pulls out the necessary info from the model.