Photon purity measurements

Based on the studies by the monojet group, we can now implement the photon purity values to estimate the QCD contribution in the single photon control region. The results of the studies are shown here:
https://indico.cern.ch/event/887731/contributions/3743260/attachments/1986452/3310163/2020-02-12_photon_cr_update.pdf

Additionally, we need to update the tight photon pt cut from 215 to 230.