AnalysisTop: fixing bug in TopObjectSelectionTools that ignores dielectron triggers

The bug is discussed in ANALYSISTO-1395. When running AnalysisTop with only dielectron triggers (as opposed to single electron, or single+dielectron triggers), the resulting electron trigger SF variations calculated are incorrect. The up and down variations of the global lepton trigger SF are found to be exactly equal to 1. This behaviour was found to be due to a check in TopObjectSelectionTools/Root/EventCleaningSelection.cxx, where dielectron triggers were not classed as electron triggers due to the '2' in the trigger name, i.e. HLT_2e vs HLT_e. An explicit check in the 'isElectronTrigger' function now addresses this and the expected behaviour is recovered.