New-style debate page

The first instalment of #555. A new design for the debate page.

![screen shot 2014-07-18 at 14 51 17](https://cloud.githubusercontent.com/assets/739624/3626852/a369610c-0e82-11e4-993b-19f0455cae21.png)

Currently only debates or speeches accessed via their ID (eg: /debates/?id=2009-10-29a.479.0) will get the new design. Everything else gets the old design.

And the new design doesn't show user-submitted annotations, or videos, yet.

The integration tests assume you have a database set up with debates from the last week of October 2009 (the only data I had to hand, in the absence of a fixture database). If you run the tests you'll see 4 failures, which correspond directly to the 3 technical blockers stopping this from being deployed:

- [ ] I can't work out how to set the `<title>` of a page via the new `Renderer` class.
- [ ] I can't get `$GLOSSARY->glossarise()` to work.
- [ ] I can't verify `$SEARCHENGINE->highlight()` works because I can't get Xapian running (see #586).

Design-wise, I think this is good enough to get out there, and iterate later – there are still rough edges, but, once some developer time is put into fixing the three issues above, I think we should deploy asap.
Whilst it doesn't always work, TheyWorkForYou currently handles two levels of heading, which you can see on e.g. http://www.theyworkforyou.com/debates/?id=2014-07-14a.561.1 ("Afghanistan" is the subsection heading, "Oral Answers to Questions - Defence" is the section heading), http://www.theyworkforyou.com/debates/?id=2014-07-14a.602.5 or http://www.theyworkforyou.com/debates/?id=2014-07-14a.649.2 - with this Pull Request, these three would, if I've understood it correctly, be presented as "Debate: Afghanistan", "Debate: Data Retention and Investigatory Powers Bill" or "Debate: Local Government".