Create IGV session files for CLE trio reporting

See https://jira.gsc.wustl.edu/browse/AT-374.
Instead of having this path hardcoded all over, we could either put it in a class level variable, or perhaps pull it from the configuration. I think it currently exists as:

`GENOME_SYS_SERVICES_FILES_URL=https://gscweb.gsc.wustl.edu/`