ACTSFW-119_DD4hep_TrackMLDetector

This merge request introduces the GenericTrackML detector (which is already described standalone in ACTS) in DD4hep description to enable consistent geometry building for both ACTS and Geant4. For now I only checked that the sensitive surfaces are on the correct position. The sensitive surfaces carry material as in the ACTS description (Silicon). However in the ACTS description the outer surface of the layer also carries material, which is already simplified. Since DD4hep describes geometry in 3D still an appropriate (even possible more detailed description) for the material needs to be implemented. This MR depends on MR !106 (merged) and should be merged afterwards. Closes ACTSFW-119.