Fix Issue #684

[jday1]

See https://github.com/airr-community/airr-standards/issues/684 for context.

Introduced GenotypeSets to allow testing of mhc_genotype_set and receptor_genotype_set.

Other minor bug fixes.

[javh]

From the call:

• Rename GenotypeSets to SubjectGenotype.
• Fine to merge for v1.4.2 after testing on iReceptor, with the understanding that the long term solution will differ.

[bcorrie]

These queries will test the deepest level objects in the MHC Genotype so are good tests to make sure nesting changes of objects don't break the structure.

curl -d '{"filters":{"op":"=", "content": { "field":"subject.genotype.mhc_genotype_set.mhc_genotype_list.mhc_alleles.gene.id", "value":"MRO:0000051"}}}' https://t1d-1.ireceptor.org/airr/v1/repertoire

curl -d '{"filters":{"op":"=", "content": { "field":"subject.genotype.mhc_genotype_set.mhc_genotype_list.mhc_alleles.allele_designation", "value":"HLA-DPB1*15"}}}' https://t1d-1.ireceptor.org/airr/v1/repertoire

[javh]

From the call:

• Good to merge after resolving merge conflicts.

[javh]

Moving this to #695, because it was less effort to fix the merge conflicts...

[javh]

Merged via #695.