changed DriftExact_track and Cavity_track to use struct args.
changed DriftExact_track and Cavity_track to use struct args.

SixTrack/SixTrackLib,hussainmkj/sixtracklib,SixTrack/SixTrackLib,dpellegr/sixtracklib,SixTrack/SixTrackLib,dpellegr/sixtracklib,dpellegr/sixtracklib,hussainmkj/sixtracklib,SixTrack/SixTrackLib