NTRs: mouse mixed strains for HCA

[paolaroncaglia]

Stemming from HumanCellAtlas/ontology#70
@pnejad needs terms to describe 2 mouse mixed strains described in GSE75659 (PMID:27668657). I’ll add them as follows:

• EFO:NEW1
  CAST/EiJxC57BL/6J
  subclass of EFO NCBITaxon:10090
  subset tag: added for HCA
  A Mus musculus individual that is a substrain of CAST/EiJ (mother) and C57BL/6J (father).
  PMID:27668657
  https://orcid.org/0000-0002-3163-0115

• EFO:NEW2
  C57BL/6JxCAST/EiJ
  subclass of EFO NCBITaxon:10090
  subset tag: added for HCA
  A Mus musculus individual that is a substrain of C57BL/6J (mother) and CAST/EiJ (father).
  PMID:27668657
  https://orcid.org/0000-0002-3163-0115

I was planning to also add axioms to represent the strains that the mixed strains derive from, but I can’t think of a way to not make the two terms equivalent, as they’d both be
derives_from EFO:0000606 C57BL/6J
derives_from EFO:0007727 CAST/EiJ
So I won’t add those axioms for now.
If a resolution is reached, it should be applied to address #18 too.

[paolaroncaglia]

@pnejad
To address one of your requests in HumanCellAtlas/ontology#70, I created the following terms:

EFO_0010945 CAST/EiJxC57BL/6J
"A Mus musculus individual that is a substrain of CAST/EiJ (mother) and C57BL/6J (father)."

and

EFO_0010946 C57BL/6JxCAST/EiJ
"A Mus musculus individual that is a substrain of C57BL/6J (mother) and CAST/EiJ (father)."

The 2 new terms will be visible in the next EFO release, scheduled for Jan 18th.