fixes #3138 - move CR library loading into initializers, only show available providers
fixes #3266 - ensures there are no duplicate notifications
fixes #3312 - support /users/extlogin as a login page based on REMOTE_USER.
fixes #3312 - support logout from REMOTE_USER-based logons.
fixes #3312 - when authorize_login_delegation_auth_source_user_autocreate is set, creates the unknown authenticated user.
fixes #3312 - tweaking nil tests; private.
fixes #3312 - add tests.