Activity Stream

Branch for activity stream commits. Still WIP. Will post comments in https://assembly.com/buckets/bounties/82 to keep it all in one thread.
I appreciate the thinking here, but would prefer to just go with the link virtual on the model for now. It would be a few lines of code and do what we need. I've spent a lot of time investigating client-server rendering patterns in JS, and IMO, it's a _lot_ of trouble. If you'd like to create a separate bounty for this and push forward, I'm happy to award, but I think it would present a big blocker on this when it's already close.