Some fixes and improvements for the DumpEvent methods

There is still an issue with DumpEventInfo, as the __str__ methods are apparently not picked up for CMSSW objects.
Investigating...
Proper implement of the print method for CMSSW objects

Small workaround put in place, since the "ROOT way" doesn't work. There is still no print method for some frequent types as
ROOT.pat::TriggerEvent
ROOT.PileupSummaryInfo
ROOT.reco::GenJet
but this is not a showstopper. We just don't see what is inside these objects.