Version 20.11.1

• added Dockerfile
• updated IGV install methods to use Makefile recipe
• added .def Singularity definition file for Singularity 3+
• removed Singularity recipe file used with Singularity 2.x and it corresponding run.Singularity.sh script
• updated the default locations for igv.jar, regions.bed, output dir, so they work better with the included container recipes
• updated Makefile with handy recipes for building and using the containers