Merge branch 'delete-metatype-entity' into 'master'

arkindex/documents/consumers.py

arkindex/documents/migrations/0031_remove_entity_metatype.py

arkindex/documents/serializers/elements.py

arkindex/documents/tei.py

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

arkindex/documents/tests/consumers/test_reindex_consumer.py

arkindex/documents/tests/test_entities.py

arkindex/documents/tests/test_entities_api.py

arkindex/documents/tests/test_tei.py