added ability to cut on maximum number of charged particles

Added ability to select events based on a maximum number of fiducial charged particles.

To generate samples efficiently for exclusive analysis we are updating this filter to allow a selection on the maximum number of charged particles from the hard-scattering interaction. Note that we left the existing NTracks property to select a minimum number of charged particles, although a more explicit name (e.g. NTracksMin) would be preferable, to ensure backwards compatibility.