Correction classes + the Demo

Correction classes + the Demo

 //
  // This is a Demo function of the general class AliTPCCorrection, which is used for
  // general space point correction due to different effects.
  // The effects used in this Demo are:
  //   1. ExB twist - general offset of the TPC axis in comparison to the B field axis
  //   2. GG error (Gating Grid volt. error) - not perfectly aligned GG voltage (in terms of voltage)
  //   3. ExBBShape - B field shape correction of the secound order
  //
  // See class descriptions for further details
  //
  // Authors: Magnus Mager, Stefan Rossegger, Jim Thomas