Add homepage

This pull request started off as just preparing for static pages like the homepage, but then I had a quiet weekend and ended up adding the whole homepage.

Questions for anybody who's more familiar with good Node patterns than me (that would be all of you):

- Is this remotely the right way of doing things for our app?
- Do we need to test any of the homepage stuff? There's not much in the way of logic.

Serious code review requested, please be ruthless. I'm not under the impression this is ready to merge and I'd like to get it done perfectly.