Addition of top pt reweighting, electron trigger and HEM

I implemented the electron trigger + top pt reweighting SFs and uncertainties. I changed the HLT path for the 2017 electrons to make it consistent with the documented SFs. I added the veto reguarding the HEM issue for 2018. I defined loose jets for reducing the number of selected events in the preselection (3 loose jets with pt > 20 GeV). I changed the definition of the lepton isolation wrt to the variables already defined in the NanoAOD samples. I fixed the b-tagging efficiency and the qcdscale/pdfalphas uncertainties bugs.