map mouse crossed genotype backgrounds to their composite parts

Currently, MGI mouse backgrounds are not mapped to their composite parts when they are some kind of result of crosses.

For example, the background "involves: 129S2/SvPas * C57BL/6" (key: 38138) should itself map to both 129S2/SvPas (key:10767) AND C57BL/6 (key:40)

This will require a fair amount of data scrubbing, regexing, etc, to get the mappings right.

I would guess that this should be put attributed the Monarch resource, as opposed to MGI, because we are the ones doing the mapping?

This may additionally need to be mapped to the GENO model.