Visualize multiple BAMs/VCFs

[robertaboukhalil]

To support tumor vs. normal comparisons, color reads differently for each BAM, with reads grouped vertically, and the bam file names on the side like in IGV

[MariaNattestad]

prefer to have file names or nicknames in the viz itself.

[robertaboukhalil]

Partly done, see https://github.com/MariaNattestad/Ribbon/issues/105 for remaining work