Add possibility to remove the production cut from region so that it uses the...

Add possibility to remove the production cut from region so that it uses the Global Range Cut instead of the default set for Regions

Geant4 will print a warning about regions without thresholds, but that is what we need. This allows one to keep regions for e.g., creating material scan with out manually having to set range cuts
As far as I can tell the threshold is only used when store_secondaries is true (which is ignored), so we are now throwing an exception if someone specifies store_secondaries without setting a threshold.
However, it seems that store_secondaries is actually never used anywhere else?