[Run2_2017_V17] Save minimal set of gen particles

Created by: aperloff

This PR adds a new way to store a collection of gen particles. Previously we were storing a very large set of particles. Now we will only save a small subset of important decays (i.e. tops, W, Z, H, etc.) We will also save SUSY particles and particles important for semi-visible jets. A flag to switch between the two methods has been added to makeTreeFromMiniAOD.

Currently this has been tested using semi-leptonic TTJets decays. The command to do this was: cmsRun runMakeTreeFromMiniAOD_cfg.py scenario=Fall17 inputFilesConfig=Fall17.TTJets_SingleLeptFromT_TuneCP5_13TeV-madgraphMLM-pythia8 nstart=0 nfiles=1 outfile=Fall17.TTJets_SingleLeptFromT_TuneCP5_13TeV-madgraphMLM-pythia8 numevents=100 saveMinimalGenParticles=True