Give controllers.Default some meat

- Add HTTP responses likely to be wanted from config/routes that
  also require no logic to return useful responses.
- Add tests!
- Add testing infrastructure for managing Play FakeApplication.
- Relegate poorly named redirect, todo, and error.
- Add 308 status.
- Add retryAfter to 429 status.
- Fix poorly spelled mnemonic for 429 status.
- Fix faulty scaladoc for redirect (wrong status code).