lrp_4.0.23

Updated drug resistance marker code to account for het genotypes. (#467)

• Updated drug resistance marker code.

• Now PfalciparumTypeDrugResistanceMarkers::CallDrugResistanceMutations pulls info directly from
  the VCF file using pysam, rather than a series of shell commands.
• Now PfalciparumTypeDrugResistanceMarkers::CallDrugResistanceMutations preserves het/hom
  genotype information in the raw output file.
• PfalciparumDrugResistanceSummary.wdl now calls into
  PfalciparumTypeDrugResistanceMarkers for
  CreateDrugResistanceSummary.
• Minor refactoring of names.

• Added VCF Index as input to PfalciparumTypeDrugResistanceMarkers.wdl
• Fixed output names in PfalciparumDrugResistanceSummary.wdl.