Added a decfile for Bu_JpsiPi,ee mode (heavily based on the mu mode)

B+->Jpsi(ee)pi is needed as it is background for the rare mode B+->pi+ee. This decfile was created by copying the mu mode decfile and essentially replacing mu with e. Tested according to the instructions in https://gitlab.cern.ch/lhcb-datapkg/Gen/DecFiles/blob/master/CONTRIBUTING.md