somatic variant calling without normal

[ericblanc20]

Is your feature request related to a problem? Please describe.
At the moment, somatic variant calling requires that each tumor and a normal sample paired with it. This is impractical for panel data, and even for some WES data.

Describe the solution you'd like
mutect2 can be used without normals, it just needs tweaks in the init file (when no normal is available, the normal bam file is left empty) and in the wrapper (the normal path & normal sample names must be left empty when no normal bam is received from the input dict).

Describe alternatives you've considered
Use germline calling, but there is no freebayes wrapper anymore (see issue #466)