Add version parameter to "restorePeristentState"

This should make handling legacy session files easier, and solves an issue with a current GWAS parameter clashing with a legacy parameter for other tracks

IGV-2059
Add test for loading session with GWAS track

IGV-2059
Remove some logging statements

IGV-2047
Change bedtools forbidEmptyOutput to true, as it should always have been

Save "forbidEmptyOutput" to session files. This is necessary because the tool spec is not re-read when a session is loaded
Merge remote-tracking branch: upstream/master