Make secondary candidate list of loci with reduced expression

[kjohnsen]

Sometimes the causative mutation will not even appear after calling variants, since nonsense-mediated decay or a mutation in the promoter region could reduce expression. In this case, we need to look at differences in expression as well. Like zy13 in the original paper.

This could be pretty complex...it would require re-reading or storing counts differently, since currently a lot of positions get thrown out from the depth and the homozygosity filters before getting stored in distance(MmapprData) as wtCounts and mutCounts dataframes