Create DO terms for groupings in MGI clusters file

[cmungall]

Of the 677 clusters in omimclusters.obo see contrib/, I can map about 2/3 of them to existing DOID classes using a mixture of label matching and jaccard coefficient of OMIM IDs in common (with a conservative threshold).

See:
https://github.com/obophenotype/human-disease-ontology/tree/master/src/experimental

The remaining ones are here:
https://github.com/obophenotype/human-disease-ontology/blob/master/src/experimental/missing-omc.obo

If these could be added to DO then we could easily make our merged disease ontology which would be wonderful.

Note: about half of these remaining ones already have OMIMPS IDs, which means this overlaps with #25