New MET correction/uncertainty tool

[cmsbuild]

This PR contains the new MET correction and uncertainty tool. It can be used for both miniAOD production and MET reprocessing on top of miniAOD.
New features :

• new pat::MET format,, takes benefit of the additional MET properties (for both corrections and uncertainties)
• 74X backward compatibility, the pat::MET format is able to read the 74X MET format and reprocess the 74X MET in 75X with e.g. new JEC. The 74X pat::MET content is empty with a 75X production.
• ME phi correction new code implemented, corrections are stored in pat::MET and can be reprocessed on top of the miniAOD
• type0 MET correction stored
• smeared MET correction stored (not up to date! still 8 TeV smearing, kept for experts)
• preparation for storage of the MET significance in miniAOD (currently not enabled per default)
• Type2 MET discarded, not supported for an analysis use
• added warning when negative JEC corrections are used in Type1MET computation

Expected changes in performances :

• size of pat::MET should be smaller than before (less uncertainty variables stored)
• no change in MET contents, physics observables are the same
• could be a bit faster than the previous tool (less modules called), but not checked

Packages changed :

• DataFormats/PatCandidates
• JetMETCorrections/Type1MET
• PhysicsTools/PatAlgos
• PhysicsTools/PatUtils

@arizzi @gpetruc, you may want to check the performances on miniAODs, let me know if you request modifications or extra checks

Automatically ported from CMSSW_7_5_X #9117 (original by @mmarionncern).

[cmsbuild]

A new Pull Request was created by @cmsbuild for CMSSW_7_6_X.

New MET correction/uncertainty tool

It involves the following packages:

DataFormats/PatCandidates
JetMETCorrections/Type1MET
PhysicsTools/PatAlgos
PhysicsTools/PatUtils

@cmsbuild, @vadler, @monttj can you please review it and eventually sign? Thanks.
@TaiSakuma, @imarches, @ahinzmann, @acaudron, @mmarionncern, @rappoccio, @jdolen, @nhanvtran, @schoef, @ferencek, @gpetruc, @mariadalfonso, @pvmulder this is something you requested to watch as well.
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@Degano you are the release manager for this.
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[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-9759/45/summary.html

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_6_X IBs (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @smuzaffar

[davidlange6]

+1