need to standardize ontology prefixes in DO

we need to make sure that all ontology sources use the same "idspaces" or prefixes for the ontologies in the xrefs/equivalence classes.

in particular, i think UMLS and MESH need updating.

UMLS is currently listed as UMLS_CUI
and MESH is listed as MSH

can these be standardized to UMLS and MESH?

(we need to make sure that all this information is consistent in the ontology as well as the data sources we ingest/massage)

also, i think these need to be documented somewhere, if not at DO, then within our Monarch documentation.