Improve the CMS example. Add word for the raw generator status of generator particles to Geant4Particle

 - changed signature of Geant4EventReader::readParticles(int,Vertex*, Particles&)
   to Geant4EventReader::readParticles(int,Vertices&, Particles& )
 - implement in LCIOEventReader, Geant4EventReaderHepEvt and Geant4EventReaderHepMC
 - for now still one vertex only is created using the first final state particle
   for HepEvt and LCIO

+ Minor changes to externilze the property/plugin mechanism.

+ Minor changes to externilze the property/plugin mechanism.

current event needs to be updated in the right place (at success)
reading the file needs to flag when the end had been reached
Issues discovered during testing

Clearer status message in moveToEvent functions, change verbosity for particle printout in HepMC, add comment