build_right_phenoplot() builds a horizontal plot displaying the mean difference in phenotype score between individuals with the alternate vs reference alleles for each SNP locus, grouped by marker group, coloured by the alternate allele frequency of each SNP. Makes use of the $Varfile phenotypic information from haplotyping object. It is an internal function called by crosshap_viz(), though can be called separately to build a stand-alone plot.
