New VariantGridColumns

[davmlaw]

Already have issue to add g.HGVS - see #890

Wrote management command "possible_variantgrid_columns" columns we don't have are:

• end
• svlen
• global_variant_zygosity__ref_count
• global_variant_zygosity__unk_count
• variantannotation__predictions_num_pathogenic
• variantannotation__predictions_num_benign
• locuscontigrefseq_accession
• variantannotationtranscript_version__gene_versionhgncuniprotpathway_interaction_db
• clinvar__clinvar_suspect_reason_code

Should we also add a way to view the new Cohort genotype columns? Eg from INFO fields etc? See how thy look, maybe we want a way to retrieve something out of the JSON specifically eg CN (custom JSON columns?)

[davmlaw]

tested ok