Add a name field on data sources

arkindex/documents/fixtures/data.json

arkindex/documents/management/commands/build_fixtures.py

arkindex/documents/migrations/0022_datasource_name.py

arkindex/documents/models.py

arkindex/documents/serializers/ml.py

arkindex/documents/tests/test_bulk_classification.py

arkindex/documents/tests/test_datasource.py

arkindex/documents/tests/test_entities_api.py

arkindex/documents/tests/test_moderation.py

arkindex/documents/tests/test_regions.py

arkindex/documents/tests/test_transcription_create.py