Merge branch 'remove-elementlink' into 'master'

arkindex/documents/admin.py

arkindex/documents/api.py

arkindex/documents/cache.py

arkindex/documents/importer.py

arkindex/documents/management/commands/import_annotations.py

arkindex/documents/management/commands/import_images.py

arkindex/documents/management/commands/import_manifest.py

arkindex/documents/managers.py

arkindex/documents/migrations/0018_remove_elementlink.py

arkindex/documents/models.py

arkindex/documents/serializer_fields.py

arkindex/documents/serializers.py

arkindex/documents/surface.py

arkindex/documents/surface_link.py

arkindex/documents/tasks.py

arkindex/documents/tests/disabled_test_edit_act.py

arkindex/documents/tests/test_annotation_list.py

arkindex/documents/tests/test_cache_db.py

arkindex/documents/tests/test_edit_elementpath.py

arkindex/documents/tests/test_edit_link.py