Give MCCollector the possibility to reject hits from not stored tracks

This is needed if we want to put an additional constraint on hits that are created by particles, which were not flagged to be stored. In this case, Gaussino will assign the same trackID to all these hits, which might be ambiguous if only one hit per particle is expected. This is also an improvement for all the future training datasets generated with Gaussino/Gauss-on-Gaussino.