Creation of header only package AtlasHepMC and migration of Generators to AtlasHepMC

Generators/AtlasHepMC/AtlasHepMC/GenParticle.h

Generators/AtlasHepMC/AtlasHepMC/GenVertex.h

Generators/AtlasHepMC/CMakeLists.txt

...s/BeamHaloGenerator/BeamHaloGenerator/BeamHaloGenerator.h

Generators/BeamHaloGenerator/CMakeLists.txt

Generators/EvgenProdTools/CMakeLists.txt

Generators/EvgenProdTools/EvgenProdTools/TestHepMC.h

Generators/EvgenProdTools/src/SimTimeEstimate.cxx

Generators/EvtGen_i/CMakeLists.txt

Generators/EvtGen_i/EvtGen_i/EvtDecay.h

...ators/EvtGen_i/EvtGen_i/EvtGenExternal/EvtPhotosEngine.hh

...ators/EvtGen_i/EvtGen_i/EvtGenExternal/EvtTauolaEngine.hh

Generators/EvtGen_i/EvtGen_i/EvtInclusiveDecay.h

Generators/EvtGen_i/src/EvtDecay.cxx

Generators/EvtGen_i/src/EvtInclusiveDecay.cxx

Generators/EvtGen_i/src/EvtPhotosEngine.cxx

Generators/EvtGen_i/src/EvtTauolaEngine.cxx

Generators/FlowAfterburner/CMakeLists.txt

Generators/FlowAfterburner/src/CheckFlow.cxx

Generators/FlowAfterburner/src/CheckFlow_New.cxx