Applied corrections to SiTracker compact descriptions that got lost after porting from examples/CLICSiD

   we need this application as it is the main simulation
   application for LC
 

IDDecoder is now independent of Readout object, instead it finds the correct readout based on the cellID / position

   - to be done: the classes describing the detectors

    - implemented copy c'tor for DetElements
    - fixed memory handling
 - fixed bug in DetectorSurfaces with 
   multiple adding of the same extensions to 
   a DetElement
 - implement gear for EcalBarrel (using DDRec::Calorimeter)

Remove debugging items from CLICSiD compact xml. First implementation of Multipole magnetic field description. Add missing units in DDG4 LCIO conversion.

 - fill for HcalBarrel in createGearForILD

First implementation of dipole field, HepMC reader for DDG4 and fix to import constants into DDG4 python