Merge branch 'demo-group' into 'master'

Makefile

README.md

arkindex/dataimport/api.py

arkindex/dataimport/tests/test_files.py

arkindex/documents/api/elements.py

arkindex/documents/api/ml.py

arkindex/documents/fixtures/data.json

arkindex/documents/management/commands/build_fixtures.py

arkindex/project/checks.py

arkindex/project/permissions.py

arkindex/project/settings.py

arkindex/project/tests/test_checks.py

arkindex/users/api.py

arkindex/users/managers.py

arkindex/users/migrations/0002_default_groups.py

arkindex/users/models.py

arkindex/users/serializers.py

arkindex/users/tests/test_registration.py