Python code cleanup by the cleanup-python-code Jenkins job.

.travis.yml

lti_consumer/apps.py

lti_consumer/lti_1p1/consumer.py

lti_consumer/lti_1p1/contrib/tests/test_django.py

lti_consumer/lti_1p1/oauth.py

lti_consumer/lti_1p1/tests/test_consumer.py

lti_consumer/lti_1p1/tests/test_oauth.py

lti_consumer/lti_1p3/constants.py

...consumer/lti_1p3/extensions/rest_framework/serializers.py

...p3/tests/extensions/rest_framework/test_authentication.py

...i_1p3/tests/extensions/rest_framework/test_permissions.py

lti_consumer/lti_1p3/tests/test_ags.py

lti_consumer/lti_1p3/tests/test_consumer.py

lti_consumer/lti_1p3/tests/test_key_handlers.py

lti_consumer/lti_xblock.py

lti_consumer/models.py

lti_consumer/outcomes.py

lti_consumer/plugin/urls.py

lti_consumer/tests/unit/plugin/test_views.py

lti_consumer/tests/unit/plugin/test_views_lti_ags.py