Converted State model to HATBM Plugins, added Contributor and Tag HATBM models, and customized HtmlReporter unit test runner.

Other Changes:
- Removed unused date fields from HATBM tables.
- Save contributors from API only if they are WordPress.org usernames.
- CakePHP console can be run from any working directory now.
- Database settings are no longer loaded during bootstrap, see AppController and AppShell now. This gives the unit tests the chance to configure the test database before settings are loaded.
- Added GitHub octicons.