Add plugin to assign Volume IDs to DetElements

[MarkusFrankATcernch]

BEGINRELEASENOTES

• Add plugin to assign VolumIDs to DetElements
  Normally this functionality id done by the VolumeManager. However, some clients prefer to not use the volume manager.
  With this plugin this basic functionality can be maintained.
• Update plugin DD4hep_DetectorDump to optionally output the accumulated volume identifiers when traversing
  the DetElement tree.

To test both, invoke e.g.:

$> geoPluginRun -input ../DD4hep/DDDetectors/compact/SiD.xml \
     -plugin DD4hep_DetElementVolumeIDs -detector /world \
     -plugin DD4hep_DetectorDump -sensitive -volids

ENDRELEASENOTES

[MarkusFrankATcernch]

@bcouturi Once merged, please check if this is what you wanted.