Update / fix MGIGene2Phenotype API

[colleenXu]

Tasks:

• Fork the parser (rename to use biothings repo): https://github.com/kevinxin90/mgi_gene2phenotype
• update the parser and data for the API https://pending.biothings.io/mgigene2phenotype/
  • fix this: the mgi.has_homolog field either has the value of "null" OR has the NCBIGene ID for the mouse gene (compare this record to this info). These are "equivalent ids", not IDs for two different genes with the homolog relationship.
  • Instead, the NCBIGene ID for the mouse gene should instead be in a field like xrefs.ncbigene

[andrewsu]

This issue is a lower priority (and this data resource is possibly obsolete) given the integration of AGR gene-disease phenotypes in biothings/biothings_explorer#260 and #28.

[andrewsu]

as noted in the previous comment, going to close this issue in favor of biothings/biothings_explorer#260 and #28