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.

Automatically ported from CMSSW_7_2_X #5188
This is an ugly protection which should not be needed. The code is clearly badly structured as this statement only applies if the jecUncertainty_ object was not initialized in the constructor.
The delete does not harm anything, but as all the code in PhysicsTools/PatUtils/plugins, it has to be fully reviewed and restructured.