MiniAOD extension for quark-gluon tagger

The QGTagger.cc plugin is updated to work also on pat::Jets and pat::PackedCandidate.
The QGTagger class is now a templated QGTagger<jetClass>, so that instead of the original QGTagger plugin, we have a QGTaggerPFJets and a QGTaggerPatJets defined.
The updated cfi fragment shows how it can be used in different situations.
The code is also a bit cleaned up to be more readable.
Users will be able to choose to use CHS and non-CHS jets, and with or without a b-jet veto. By not introducing a default parameter for those two, I force people to think about on which collection (srcJets) they apply the tagger, and to select the appropiate jetsLabel with it.
The other parameters should not really be changed on the user side, so I put them here as default.