Add HBSM discriminant variables

Add functions to discriminate at between ttbar and H+.

• Invariant mass between the J and the lading b in all 1J regions.
• Invariant mass of H+ from the leptonic top and the leading b (ref. https://indico.cern.ch/event/594431/contributions/2402714/attachments/1387211/2111474/Hplus_12Dec2016.pdf)