Changes needed to migrate AthGeneration to HepMC3 (part I)

In this merge request:

• the pointers to HepMC particles and vertices are now typedefs GenParticlePtr and GenVertexPtr, the same name as smart pointer types in HepMC3. This change is propagated across packages but 2-3 special cases, e.g. for the GeneratorFilters some codes will be rewritten significantly, so there is no point in changes now.
• barcode and some other functions are introduced. These are inlines for HepMC2-based AtlasHepMC (i.e. current version) and for HepMC3 version of AtlasHepMC an implementation will be provided in a separate merge request.
• Replaced CLHEP vectors with native HepMC vectors

Technically the changes are just replacements of

• GenParticle* to GenParticlePtr, GenVertex* to GenVertexPtr , etc. These will match in most cases the HepMC3 types.
• outdated constructors like new HepMC::GenEvent(int,int) with free functions HepMC::newGenEvent(int,int) that are implemented in future MR in HepMC3
• outdated member functions like barcode are implemented as free functions/templates with the same name in HePMC namespace.

12:55, 26.03: so far marked as WIP, needs some testing. 14:14 07.04: removing WIP 24.05 removing WIP and prepare for a merger Tagging @akraszna @ewelina @jchapman