Add eQTL effects and non-eQTL group effects to simulated means matrix. The eQTL effects are incorporated using the following equation: $$Ygs = (ESg x Mgs x Gs) + Mgs $$ Where Ygs is the mean for gene g and sample s, ESg is the effect size assigned to g, Mgs is the mean expression assigned to g for s, and Gs is the genotype (number of minor alleles) for s. Non-eQTL group effects are incorporated as: $$Ygs = Mgs x GEg$$ Where GEg is the group effect (i.e. differential expression) assigned to g. To simulate multiple gene mean matrices with different group effects, this function can be run with `id` designating the group id.