update filters; add pileup element fields and filters

- Updated filters to be >= rather than >
- Added EdgeDistance filter to drop bases closes to the edge of the read
- Added MinLikelihood filter to filter Genotypes with low likelihood
- Added nearbyMismatches function to pileupelement to skip elements within many SNVs nearby
- Removed strand bias filter from GenotypeFilters for now as those fields were removed from ADAMGenotype