Add Mammalian Phenotype Ontology

[gaurav]

This PR adds terms from the Mammalian Phenotype Ontology as requested by CAM-KP (#240). As a first stab, I added just the IDs but no extra concords. This results in a bunch of single-ID PhenotypicFeature cliques that mirror existing cliques, such as:

• MP:0001914 "hemorrhage" duplicates NCIT:C26791 "hemorrhage", which includes MESH and MEDRA identifiers.
  • We might be able to use EFO to make this connection, but UberGraph doesn't contain this edge since UberGraph doesn't have EFO.
• MP:0003342 "accessory spleen" duplicates HP:0001747 "Accessory spleen"
  • UberGraph has a triple that indicates that HP:0001747 rdfs:subClassOf MP:0003342, and as a result UberGraph knows that MP:0003342 is a subclass of HP:0001743 "Abnormality of the spleen"
• TODO: add more

Closes #240.

WIP. Should be merged after PR #279.