python/sixtracklib: renames the num_particles field of NS(SpaceCharge*) elements back to number_of_particles
python/sixtracklib: renames the num_particles field of NS(SpaceCharge*) elements back to number_of_particles

SixTrack/SixTrackLib,SixTrack/SixTrackLib,SixTrack/SixTrackLib,SixTrack/SixTrackLib