fixes to genotyping model to use negative binomial distribution, never Poisson
remove option to do het calling (but leave in code so would be relatively easy to add at a later date)
require cluster_vcf_records 0.13.1, which can use vcflib binary - install this in container using apt instead of build from source (which was proving troublesome)
vcflibbinary - install this in container usingaptinstead of build from source (which was proving troublesome)