Minor HHbbgg updates

There a few updates:

• Save n_electron, n_muons, M_X, mvaID of leptons
• Rearrange the calculation of chi_t0 and chi_t1. Previously, it was calculated before the selection of b-jet candidates
• Store index of b-tagged jet, VBF-tagged jets so to track back which of the jets in jets collection is selected as b-jets or VBF-jets
• Store sum of weights before and after applying b-tagging SF weight, which are needed for proper normalisation in post-processing scripts
• Handle argsort when there are no objects (leptons, fatjets, etc) present in a chunk of the file