LHCBGAUSS-1351 Updating particle properties for EvtGen Pythia decay model

Port merging of branch 'LHCBGAUSS-1351'
See merge request !267 (merged) for 'Sim09'

(cherry picked from commit d405d119)

9389f4a0 Updated EvtPythiaEngine to correctly handle updates of various particle
28ed8ea3 Implement most of the code review suggestions.