Merge branch 'allowed-metadata' into 'master'

arkindex/documents/admin.py

arkindex/documents/api/elements.py

arkindex/documents/consumers.py

arkindex/documents/fixtures/data.json

arkindex/documents/migrations/0029_allowedmetadata.py

arkindex/documents/models.py

arkindex/documents/serializers/elements.py

arkindex/documents/serializers/light.py

arkindex/documents/tests/consumers/test_corpus_consumer.py

arkindex/documents/tests/test_elements_api.py

arkindex/documents/tests/test_metadata.py

arkindex/project/api_v1.py