- enabling this code breaks some tests in the examples
   so we disable it for now

   => to be fixed next year

 - still need resolution for failing tests
  - or revert to old treatment of elements ...
 - release notes created from
    git log --pretty=format:"%aN %ad %n  - %s" --date=short
   => should have squashed commits with more
   meaningful commit notes in the future ...

add map cellID of surface <--> vector of cellID of neighbouring surfaces for ZPlanar and ZPetalDisk data struct

 - also set DD4HEP_LIBRARYPATH in dd4hep_add_library_path()
 - export ROOTSYS if it has not been set
    ( assumes path_to_ROOT/cmake )