Refactoring all instantations of DRSTree().
DRS() becomes CmipDRS() to indicate we will have multiple subclasses of BaseDRS().
Abstracting away CmipDRS.
Make the DRS Scheme theoretically switchable within drs_tool
Refactoring
Fixing hidden test
Test for drs.update()
Fixing DRS.update()
First functioning CORDEX Test.  We are in business!