- see ILDExDet/src/ILDExVXD_geo.cpp and
     ILDExSimu/src/test_surfaces.cc as examples
     on how to use them
  - moved example test_surfaces to ILDExSimu 
     ( tests if hits created in simulation are on the surface)
  - fixed Surface::distance and Surface::insideBounds to
    call the correct methods for planes and cylinders
    ( handles are not polymorphic -> might be better to change
      VolSurface into plain class )