Store trigger names in metainfo

Is is currently difficult (for me) to figure out which dimuon triggers are 1) available and 2) used. The code in applyDiMuonTriggerStrategy uses magic numbers 0 and 1 and the Ntuplizer is too generic to figure out what they mean.

I think the list of triggers should be stored in the metainfo and trigger code should refer to them by name.