this UserAction derived class is to implement catches to known bugs in Geant4 that require grabbing const G4 objects and altering them - a very bad idea in general. Please do not add to this class without discussing with the LArSoft Conveners
this UserAction derived class is to provide a hook during G4 stepping in which to call the code that calculates the number of ionization electrons and scintillation photons produced by each step