such that other user actions can access it (e.g. for adding the MCParticle collection)

    - renamed namespace tgeo to dd4hep
       -> users need to replace tgeo::mm by dd4hep::mm

Hopefully I got the assemblies right now. Assembly test added in examples/ClientTests. Please see also doc/release.notes

   -D DD4HEP_USE_LCIO=1 ( -D LCIO_DIR=_lcio_install_dir_ )
     - LCIO_DIR is not needed when iLCSoft is initialized

   -D DD4HEP_USE_BOOST -D BOOST_ROOT=_path_to_boost_
 - client packages will automatically also use boost
   ( add_definition( DD4HEP_USE_BOOST ))