Split everything into SQL files

arkindex/documents/export/__init__.py

arkindex/documents/export/classification.sql

arkindex/documents/export/element.sql

arkindex/documents/export/element_path.sql

arkindex/documents/export/entity.sql

arkindex/documents/export/entity_link.sql

arkindex/documents/export/entity_role.sql

arkindex/documents/export/image.sql

arkindex/documents/export/metadata.sql

arkindex/documents/export/structure.sql

arkindex/documents/export/transcription.sql

arkindex/documents/export/transcription_entity.sql

arkindex/documents/export/worker_version.sql