shows all DetElements in model incl. #surfaces

   we need this application as it is the main simulation
   application for LC
 

   a DDG4 based simulation with xml configuration files
   (originally in DDSim)
 - renamed print_materials.cc to print_materials.cpp

 - added simple utility print_materials.cc 
 - started to implement averaging materials for surfaces
    - issue with ILDExDet geometry and assemblies ...

 - added drawing of LCIO events to teve_display 
   - so far only SimTrackerHits ( tbc) 

 - new method Surface::getVertices() (only planes so far)
 - added some convenient methods to Vector3D

DDCore and other packages now depend on DDSegmentation
Segmentation from DDCore now holds a DDSegmentation object that is created during XML parsing
Readout interface extended to act like a full IDDecoder combining information from the volume manage and the DDSegmentation object
TODO: Segmentation could be removed completely, if Readout simply holds a DDSegmentation object
TODO: Missing DDSegmentation classes for cylinders

    - DDExamples no longer built with DD4hep
      => will become standalone packages
    - moved UtilityApps from DDExamples to root level
      apps are built by default
    - create DD4hepConfig.cmake