Spike of lightbox cheat cards

This is a quick :airplane: spike of the cheat cards variant of #185.

It adds a right sidebar, similar to the ToC sidebar with a single link in it that opens in a [facebox](https://github.com/defunkt/facebox). I literally picked this by opening a modal on GitHub.com and clicking inspect element. In my limited experience with jquery plugins, it looks pretty legit.

I pushed this branch to the RailsBridge fork so any other maintainers can run with this while I'm afk.

Things I want to see before this is considered for merge

- [ ] That (popout) link needs to become an icon
- [ ] It'd be really hot if the cheat bar, and ToC for that matter, were fixed and scrolled with you no matter where you were in the page.
- [ ] Actual content needs to go in the links.

We can facebox other random pages, pages on the instalfest site, or fragments of the current page. So anything goes.