add medgen disease id mappings

[nlwashington]

please add medgen ids to the uberdisease ontology for xrefs. these will be useful for linking with clinvar data.
http://www.ncbi.nlm.nih.gov/medgen/docs/faq/#rel

also found this possibly relevant:
ftp://ftp.ncbi.nih.gov/pub/medgen/MedGen_HPO_OMIM_Mapping.txt.gz

ftp://ftp.ncbi.nih.gov/gene/DATA/mim2gene_medgen

also see related monarch-initiative/disease-miner#5
and https://support.crbs.ucsd.edu/browse/NIF-11766

[nlwashington]

Also note that the medgen-to-omim (and other vocab) mappings here can't be trusted as equivalence classes. For example, for Hermasky-Pudluck syndrome,
http://beta.neuinfo.org/mynif/search.php?q=DOID_3753&dis=Hermansky-Pudlak%20syndrome&t=indexable&nif=nlx_151671-4&b=0&r=20
it has several subtypes; each one maps to GeneReviews:NBK1287, which is for a general type of Hermansky-Pudlak.

[mellybelly]

yeah i think i would want to manually review all medgen xrefs...

[cmungall]

This issue was moved to monarch-initiative/monarch-disease-ontology-RETIRED#8