Protection against crazy tracks; correct assignment operator; extended generator functionality; external decayer for polarized Lambda hyperons.

added FusedSil to media.geo, fixed N2; added pads and some fixes of field cage position in TPC geometry

- create_rootgeom_zdc_oldnames_7sect_no_central_module_v1.C: cleared
  unnecessary comments and obsolete descriptions. Material inside scintillators
  in FHCal modules have been changed from FscScint to the polysterene which is
  closer to the real one used in FHCal.
- Added WALL geometry file create_rootgeom_wall_vacuum_no_hole_oldnames_v1.C

It produces a separate file dubbed as mpddstXXXX.MiniDst.root in which  
the MiniDst format for reconstructed events used.