Support prerendering pages

The lib/server file now supports prerendering using jsdom instead of phantomjs (there are a bunch of reasons why this is better/awesome, so let me know if you're curious) and the staging environment is now set up to *sometimes* send requests to this backend process via passenger. Aside from some issues with the application code, things work well enough that after introducing some caching I think we may choose to consider enabling this for *all* clients.

I've also added the link rel=canonical tag so that facebook will start pulling OG tags correctly and google will stop indexing for now.