R1:4bc561f17bc8

Make Conpherence threads update in real time, very roughly

Summary:
Ref T4083. This needs some work (mostly in the Conpherence JS itself), but is sort of functional. In particular:

- On thread pages, add the thread as a `pageObject`.
- After updating a thread, send a new "message" event to the server.
- Share a little more event posting code.
- In the browser, use event dispatch to respond to events.
- Add a listener for the new event type.
- Update conpherence threads (this part is really…