Update JetTrackParticleThinning to use MT thinning.

In some cases, JetTrackParticleThinning was used with an AND following
a TrackParticleThinning.  This doesn't work directly with the
MT thinning scheme.  Instead, extend JetTrackParticleThinning to take
a selection string for the track particles as well, and move the
selection there.