implementing tth vars and model in Yibo's C++ framework

[irenedutta23]

• plot input vars for sig HH and bkg ttH and compare with Thomas's plots
• If vars look ok, implement model evaluation in C++ framework. Only evaluate on even event numbers for ttH bkg and ggHH sig. Evaluate on all events for remaining samples.
• Fix plotting script - make official looking CMS plots and add ratio panels to the bottom. Add all samples in plots.