Remove unused controllers
Move build number to larger indicator
Ensure only a single streaming connection is active

Summary:
This implies the frontend is aware of the stream names on the backend. In
the future we should adjust it so the frontend can just pass it a list of
API endpoints (or IDs?) to subscribe to events.

Reviewers: cf

Reviewed By: cf

Differential Revision: https://tails.corp.dropbox.com/D40085