Add a plugin to clean HLT jets against leading leptons

Add a template class `HLTJetsCleanedFromLeadingLeptons` that cleans HLT jets against a desired number of leading leptons extracted from results of a lepton filter. Logic of the new plugins differs a lot from [HLTJetCollectionsForLeptonPlusJets](https://github.com/cms-sw/cmssw/blob/CMSSW_7_1_0_pre9/HLTrigger/JetMET/src/HLTJetCollectionsForLeptonPlusJets.cc), which, for each lepton in a given collection, produces a dedicated collection of jets, cleaned against that lepton only.

The new class is needed for updated single-top paths.