Automated allele linking

At the moment, there may be variants from both genome builds that share an allele but don't know it.

We run a check on the allele page, but it would be good to get this in the general case.

Perhaps after doing an import, or nightly, looking at new imports that day, we look for all alleles with ClinGen for the opposite build of the new imports, and see if they match the new variants.