Cleanup setPriorVcf

[lima1]

setPriorVcf grew organically and cutoffs are ad hoc and might not work well for all combinations of germline and somatic databases and their corresponding versions.

• [ ] Use population allele frequencies, PoN counts and COSMIC counts jointly when available (e.g. cases with high allele frequencies are wrongly set to a prior of 0.5 when found in COSMIC with >= 6 counts, despite being also found in the PoN).