v0.9.0 - storage*: Drop intermediary conversion step into OriginVisit - pg: use 'on conflict do nothing' strategy for duplicate metadata rows. - Make the code location of metadata endpoints consistent across backends. - Add content_metadata_{add,get}. - Add context columns to object_metadata table and object_metadata_{add,get}. - Generalize origin_metadata to allow support for other object types in the future. - Work around the segmentation faults caused by pytest-coverage + multiprocessing.