Fix DD4hep_DetectorDump plugin to avoid crash. Add test to check if DetElements have proper placement set

LCIO now exports LCIO::lcio, so we could use that if LCIO is new enough

Explicity set namespace to TrackClassification in
TestStackingAction::classifyNewTrack

Co-authored-by: Andre Sailer <andre.philippe.sailer@cern.ch>

Co-authored-by: Andre Sailer <andre.philippe.sailer@cern.ch>

Co-authored-by: Andre Sailer <andre.philippe.sailer@cern.ch>

Remove support for very old versions of ROOT < 6.26.0. Remove default use of std namespace from some implementation files.

Remove support for very old versions of ROOT < 6.26.0. Remove default use of std namespace from some implementation files.

Remove support for very old versions of ROOT < 6.26.0. Remove default use of std namespace from some implementation files.

Remove support for very old versions of ROOT < 6.26.0. Remove default use of std namespace from some implementation files.