Start moving tests over to the new framework, and a few bugfixes

* [app] Show the name of entities that could not be found in the error
* [blueprints.entity] Swap `entity.profile` and `entity.profiles`
* [documents.profiles] Output servers in to_json()
* [tests]
  * Skip url_for if the endpoint starts with a /
  * Added _external argument to profile_url_for()
  * Moved response_has_link_header() here
* [tests.test_app] Cleaned up using newer functions