Bump to Django 3.1

Dockerfile

Dockerfile.binary

arkindex/dataimport/migrations/0016_new_jsonfield.py

arkindex/dataimport/models.py

arkindex/dataimport/serializers/workers.py

arkindex/documents/api/entities.py

arkindex/documents/api/ml.py

...dex/documents/tests/consumers/test_ml_results_consumer.py

arkindex/project/config.py

arkindex/project/polygon.py

arkindex/project/tests/config_samples/defaults.yaml

arkindex/project/tests/config_samples/override.yaml

arkindex/project/tests/test_config.py

base/requirements.txt

requirements.txt