Merge branch 'fix/api-tests-and-pep8' into 'develop'

app/apps/api/serializers.py

app/apps/api/tests.py

app/apps/api/urls.py

app/apps/api/views.py

app/apps/core/models.py

app/apps/core/tasks.py

app/apps/core/tests/factory.py

app/apps/imports/models.py

app/apps/imports/parsers.py

app/apps/imports/tasks.py

app/apps/imports/tests.py

app/apps/imports/urls.py

app/apps/users/models.py

app/apps/users/tests.py

app/apps/users/urls.py

app/apps/users/views.py

app/apps/versioning/models.py

app/apps/versioning/tests.py