Cleanup OpenIDTeams support

- Namespace the session attribute name ('groups' => 'openid.teams')
- Update CHANGES.rst, README.rst
- setup.py: Add python-openid-teams to extras_require
code cleanup

Rename session to oidsession to reduce confusion with the trac session
Update team/group membership on every log-in
Security: don't create users with a username which has preexisting trac permissions
Delete TracAuthOpenId.egg-info/trac_plugin.txt

This has not been required since trac 0.8.
Update .gitignore