- implemented for the VXD

   Gear objects from DetElements with 
   data structures holding relevant information
   

    - renamed namespace tgeo to dd4hep
       -> users need to replace tgeo::mm by dd4hep::mm

   - only build if DD4HEP_WITH_GEAR=1

  - fixed  geometry in ILDExVXD_geo.cpp, ILDExTPCSIT_geo.cpp
     wrt. to position of support ans sensitive ladders
  - added test_convert_ild_gear 
  - updated release notes

 -  new wrapper object GearHandler that can be used
    to add GearParametersImpl objects as extension
    to DetElements
 - factory method createGearMgr( LCDD& lcdd )
 - simple program convertToGear
 - so far only TPCParameters added to ILDExDet...