Remove frontend routes, views and controller.

Contact detail pages are no longer served by this application, so having them
here is confusing as they are no longer in sync with the frontend app.
Helpers for frontend paths.

Enable linking from admin page to frontend, and also from frontend index page
(which is still served by this app for now) to the detail pages.
Remove test for deleted functionality.
Merge pull request #156 from alphagov/remove_frontend

Remove frontend code for leaf pages