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 didn't like what I was doing here (or what I had to do here) either. In general I was hoping to have some link and url helpers available to do something like: `link_to admin_user_path user`. More on that in response to your other comment.
Regarding the escaping and using SafeString, I understood that because I'm using SafeString, I need to do the escaping (since SafeString expects a _safe_ string).
See the link helper example on http://handlebarsjs.com/, where it says:
> Handlebars will not escape a Handlebars.SafeString. If you write a helper that generates its own HTML, you will usually want to return a new Handlebars.SafeString(result). In such a circumstance, you will want to manually escape parameters.