Add user deactivation

tests/commands/test_user.py

tests/models/test_invite.py

tests/views/test_api.py

tests/views/test_oauth2.py

tests/views/test_selfservice.py

tests/views/test_services.py

tests/views/test_session.py

tests/views/test_signup.py

tests/views/test_user.py

uffd/commands/user.py

uffd/migrations/versions/23293f32b503_deactivate_users.py

uffd/models/invite.py

uffd/models/service.py

uffd/models/user.py

uffd/templates/role/show.html

uffd/templates/service/show.html

uffd/templates/user/list.html

uffd/templates/user/show.html

uffd/translations/de/LC_MESSAGES/messages.mo

uffd/translations/de/LC_MESSAGES/messages.po