Preparatory changes for the HepMC3 migration for packages in AthSimulation

This merge request mainly makes the following replacements for classes which are part of the AthSimulation project:

HepMC::GenParticle* --> HepMC::GenParticlePtr
const HepMC::GenParticle* --> HepMC::ConstGenParticlePtr
HepMC::GenVertex* --> HepMC::GenVertexPtr
const HepMC::GenVertex* --> HepMC::ConstGenVertexPtr

Plus a few other syntax replacements to use helper functions defined in AtlasHepMC/GenParticle.h and AtlasHepMC/GenVertex.h. The purpose is to prepare for the migration from HepMC2 to HepMC3. Further syntax changes will be required.

Simulation/G4Utilities/G4UserActions/src/AthenaTrackingAction.cxx

@@ -46,7 +46,7 @@ namespace G4UA
     {
       // Why a const_cast???
       // This is an ugly way to communicate the GenParticle...
-      HepMC::GenParticle* part =
+      HepMC::GenParticlePtr part =
         const_cast<HepMC::GenParticle*>( trackHelper.GetTrackInformation()->
                                          GetHepMCParticle() );