Merge branch 'remove-image-datafile' into 'master'

arkindex/dataimport/admin.py

arkindex/dataimport/api.py

arkindex/dataimport/serializers/files.py

arkindex/dataimport/tests/test_datafile_api.py

arkindex/dataimport/tests/test_files.py

arkindex/documents/fixtures/data.json

arkindex/images/migrations/0003_remove_image_datafile.py

arkindex/images/models.py

arkindex/images/serializers.py

arkindex/images/tests/test_image.py

arkindex/images/tests/test_image_api.py