Hepmc3 nightly fixes 13122020 part 1

Andrii Verbytskyirequested to merge
averbyts/athena:hepmc3_nightly_fixes_13122020_part_1 into master

In this MR:

  • Use с++11 loops for the HepMC3 compatibility
  • Use Genparticle*->GenParticlePtr and similar
Edited by Andrii Verbytskyi

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