Upsert and delete support (#20) * fix for bad query to get asset ids * fix for bad insert_timestamp sparql * extract source_id and source_id_type ready for delete * added delete methods for UPSERT * fixes * fixes * send delete to index service * tidy up * do real deletes * fix delete queries * only update exact asset matches * id and id_type encoding fixes * crude fix for time slip between services server and blazegraph. NOW() is used on lastmodified insert, but python time used in query * first attempt at wiring up DELETE * deletes fixes * Bumped version