FixMe.txt

- Length units are different between TGeo and G4. 
  The conversion VGM takes care of it but the detector constructor drivers should create the TGeo geometry in unit of cm which is not the case today.
- DetectorElement should be associated to one and only one volume placement
- Overlap problems between 'tracking_volume' and TPC. We need to rethink the need for the tracking volume
- Workout sensitive volumes
- DetectorElement sould associated to assembies if they do not provide an emvelop shape.