Integration of MVA/NoPU MET in central release

This PR contains the MVA and NoPU code the JetMET group wants to make available centrally, and eventually computed at the RECO and miniAOD level after discussion with the RECO/AT group.

This PR add the package RecoMET/METPUSubtraction, and add the pat configuration files needed for the MET uncertainty tool.
Several fixes and cleaning are also done on the patCaloMET configuration, the pileupjetid configuration, the pileupJetid training needed by the MVA and NoPU MET.

If I remember well this was a first attempt to use trainings in a database, so names were the same probably for the sake of simplicity.
In the few cases I had to use a PoolDBESSource, all labels were untracked, so I think this is something more general as well, but I have no more details.