first version of cluster position calculation on the chamber local

first version of cluster position calculation on the chamber local
coordinate system
  - x position calculation based on iterative drift time calculation
    taking into account diffusion and tails from previous clusters in the
    tracklet. Drift velocity corrected for drift length
  - y position calculation based on gaussian approximation of PRF and
    secondary effects (diffusion and tracklet angle)
  - documentation and implementation formulae
  - TODO : tests, parameter calibration, link to recoParam(?)