pytest: Fix the user login function.
- Pyramid doesn't expose the session as pylons does it as `response.session`
- Therefore we have to look it up in the environ.
pytest: Use hardcoded login URLs in tests.
- It's not so easy to use pyramids URL generation methods from within the tests.
- Therfore we hardcode the URLs.
login: Fix password reset mail link.
- Pyramid needs the request object to generate an URL.
- Therefore we generate the URL in the view and pass it to the model
to send the email.
