Added role moderator groups and extended invites to support delegation

...s/5cab70e95bf8_invite_creator_and_role_moderator_group.py

tests/test_role.py

uffd/default_config.cfg

uffd/invite/models.py

uffd/invite/templates/invite/list.html

uffd/invite/templates/invite/new.html

uffd/invite/views.py

uffd/role/models.py

uffd/role/templates/role.html

uffd/role/views.py

uffd/session/views.py

uffd/user/models.py