Beam pipe driver modified, and additional field (with default value) added, that controls the placement of the core (made of beam material), in order to be able to add several BP walls made of various materials

if the macro is called from other libraries this variable might be set and should be used for consistency

Implement dd4hep::Tube using TGeoTubeSeg (See also Issue https://github.com/AIDASoft/DD4hep/issues/203)

Implement dd4hep::Tube using TGeoTubeSeg (See also Issue https://github.com/AIDASoft/DD4hep/issues/203)

Separate placement calls in the VolumeManager and distinguish between DetElement placements and Volume placements (currently unused)

DetectorData: Warn if a second object (e.g., constant) is created, as insert will not overwrite the existing one