Make Bouncer use type instead of http_status

- Edit the tests so they specify both http_status and type, so we don't
  get all sorts of failures about not nullable columns.
- Fix some whitespace to line up blocks of its(:foo) { ... }.
Fix red tests

* Rack doesn't know about :type, so let's not test for it
* Mapping should_receive only :type now (will error if we say it's going to
  receive :http_status and then it doesn't)
Update db/structure.sql from transition's copy, so it includes type
Be consistent in referring to archives and redirects as status codes
Merge pull request #71 from alphagov/change_http_status_to_type

Use the type column instead of the http_status column