reduce the amount of common hits  to be found to Prune track candidates (delete duplicates)
fundamental changes:

now a track is described by a list of TrackStateImpl records, which specify track parameters at every volume (sensitive so far) and track point on the volume surface (Local frame!!)

GBL trajectory and fit is performed and GBL corrections are applied to the TrackState records to improve the knowledge of the track trajectory (should not change with iterative GBL fit)