Implemented device login for OAuth2 authorizations

migrations/versions/a8c6b6e91c28_device_login.py

tests/test_oauth2.py

tests/test_session.py

uffd/oauth2/models.py

uffd/oauth2/views.py

uffd/session/models.py

uffd/session/templates/session/deviceauth.html

uffd/session/templates/session/devicelogin.html

uffd/session/templates/session/login.html

uffd/session/views.py

uffd/templates/base.html