Add setting for configuring output of PGUN simulation (@adavis)
See merge request !2385 (merged) (cherry picked from commit a95d551b)
Needed to propagate pGun PV from Gauss through the Moore, Brunel and Stripping processing steps for 2018 pGun productions with Gauss v54r0 (Sim10) and Gauss v49r16 (Sim09) or later. To be activated for steps that process pGun, by setting SimConf().pGun=True