Geant4Output2LCIO: Use event and run number offset also in the case of presence of input event parameters extension

Geant4Output2LCIO: get LCIO input event parameters from dedicated event extension (if exists) and write them to LCIO output event

Added run and event number offsets to start counting runs and events from a different value than 0. Added float, int and string event parameters to class properties allowing a steering from outside

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

 - add all parentless particles to outgoing vertex

if the hit is produced by a particle that is not kept in the MCParticle history we set the bit
added originalG4ID to Geant4Particle class for faster lookup, as this ID is stored with the hit
Otherwise we need a complicated and time-consuming logic to parse the equivalent map if this hit really belonged to that track

Add test to dump hits from MultiSegment-MultiCollections example. Investigate issue: https://github.com/AIDASoft/DD4hep/issues/141 for details

 - 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

   - note: this does not yet seemt to be filled by DDG4!

Add DDRec/src/plugins to folders documented by doxygen

Add groups for plugins and some example
Add an entry in the main "Modules" part of the doxygen website so they are easily found.
And sub groups for different plugin types.
See changes in the plugins for example. The documentation in these changes is not complete.