[cleanup] Fix flake8 errors in web/application.py and associated test

[test] Simplify CWTC's init_authentication and assertAuthSuccess which shouldn't rely on removed .session attribute while it's not necessary and could be written in a simpler way.

[cleanup] Drop non sense sentence in docstring

[repo] Drop Session at last This is not used at all anymore.

Fix flake8 some errors

[test] Use existing reference to repo_source

[repo] Drop repo.new_session method we should not go through Session to create Connection anymore. This is unofficial API, no backward compat for now.

Stop using Session on the repository side Only expect session on web request, and let the web session/authentication managers provide them. Access to cnx.data, which used to return session data, is deprecated: there is no more access to session data from the repository side, and they should be access from req.session.data from the web side.

[test] Drop unnecessary call to new_session This is not unittest, the above call is enough.

[user] Drop ugly hack on CWUser entity class which should be not necessary anymore, beside two remaining usage in our own test suite.

[test] Use user_session_cache_key function to generate cache key.

[session+test] Stop storing / accessing session when it's not necessary

[devtools] Stop relying on Session to create connection in RepoAccess

[devtools] Stop using repo.new_session

[session] Kill support for a 'session_open' hook event To be consistent with dropping of the 'session_close' event, and also because this is already not called when using pyramid.

[devtools] Rename FakeSession into FakeConnection because it is what it is.