Make AthSimulation more compatible with HepMC3
Make AthSimulation more compatible with HepMC3
- removal of FourVector::rho()
- removal of inlined forward declarations. --> forward headers.
- adding some headers explicitly
- use HepMC::Print compatible with HepMC2 and HepMC3
Tag @jchapman
Edited by Andrii Verbytskyi