combine all VolIDs from all parent volumes
     in the path to the current sensitive volume
    - used in Geant4CalorimeterSD and 
      Geant4TrackerSD

  
  - added new method:
    long long Geant4SensitiveDetector::getVolumeID(G4Step* step)
  
  - use it in Geant4Tracker(Calorimeter)SD
  
   - changed ILDExEventAction to extract the correct 
     readout string from lookup via cellID
 

     start with the least significant bit
     (the 'lcio' convention)
   - unused hight bits are still all 1
     this is 'cured' in BitField64.setValue() 

   => ideally we should try an use 0 as default value
      for the IDDescriptors and unused bits
      this would allow to directly use the 
      VolumeID of the sensitive volume as cellID
      for the hits
   ( I did not manage to get this working, though.)

   - using the VolumeID set for PlacedVolumes to be the
     superset of the physVolIDs of the complete 
     path from the world volume
     - as the internal encoding in DD4hep starts with
       the MSB we have to transfer it into the LC
       convention using the BitField64 class

     -> see code in Geant4TrackerSD
        ( should go to a standalone/utility function)
   
   - adopted VXD and SIT to set the complete
     set of the canoncial cellID: system,side,layer,module,sensor


--Ths lin, and those below, will be ignored--

M    DDG4/src/Geant4TrackerSD.cpp
M    DDExamples/ILDExDet/compact/ILDEx.xml
M    DDExamples/ILDExDet/src/compact/ILDExSIT_geo.cpp
M    DDExamples/ILDExDet/src/compact/ILDExVXD_geo.cpp

 - changed to use standard way of finding geant4 with CMake:
   -D Geant4_DIR=_path_to_Geant4Config.cmake 
   (this script provies also the dependencies used to build geant4)

   cellIDs to SimTrackerHits in ILDExSimu
   - use ILDCellIDEncoder (needed for MarlinTrk)
   - uses the G4PhysicalVolume CopyNo
   - so far only SIT and VXD
     TPC hits still missing cellIds (and row-volumes)

  - added Property $Id$ to all *.h *.cpp and *.xml files
    to allow versioning with SVN

   filled from CopyNO
 - added edeposited to TrackerHit
 - reduced some debug printout
   (#define DEBUG 0)