New low-energy gamma-nuclear final-state model

A new gamma-nuclear final-state model, G4LowEGammaNuclearModel, based on precompound de-excitation, is used below 200 MeV, while Bertini cascade is used above 199 MeV up to 6 GeV, and QGSP above 3 GeV.

This applies to all reference physics lists, with the only exception of ShieldingLEND, where G4LENDorBERTModel is used below 20 MeV, and Bertini is used above 19.9 MeV (as usual, up to 6 GeV, and QGSP above 3 GeV, while G4LowEGammaNuclearModel is not used at all in this case).