New variant calling tools need WDL tasks

[mark-welsh]

Will be adding:

• Strelka2, an Illumina tool for somatic SNV/Indel calls; tumor normal compatible
• Manta, another Illumina tool for SV calls
• Control-FREEC, for CNVs (this is has an interesting runtime setup)
• MuTect2 (GATK4)
• LoFreq