HeavyIon: Add E/p cut to electrons and extend event content for electron collections.

[harmonicoscillator]

This PR adds an E/p cut of <2 to the Heavy Ion electron reconstructions chain. The reason for this cut is to remove fake jets which arise from low-pt (very-curved) tracks attached to high pt ecal clusters. Theses "electrons" are then included in jets, but since the track is very curved the ecal cluster is not actually inside the jet.
Please see motivation slides here:
https://twiki.cern.ch/twiki/pub/CMS/PhotonAnalyses2015/20150825_fakerate.pdf
Additional documentation can be provided on request.

Additionally, this PR includes two additions to the Heavy Ion Event Content for electron-related quantities.

This PR should not affect pp workflows in any way.
Matrices 5.1 and 140.53 worked locally for me.

This will also be backported to 7_5_X.

This PR supersedes @doanhien PRs #11193 and #11191, both of those should be closed.

[harmonicoscillator]

75X backport PR is #11224

[cmsbuild]

A new Pull Request was created by @richard-cms (R. Alex Barbieri) for CMSSW_7_6_X.

HeavyIon: Add E/p cut to electrons and extend event content for electron collections.

It involves the following packages:

RecoHI/Configuration
RecoHI/HiEgammaAlgos

@cmsbuild, @cvuosalo, @slava77 can you please review it and eventually sign? Thanks.
@MiheeJo, @jazzitup, @echapon, @yenjie, @kurtejung, @istaslis, @mandrenguyen, @dgulhan, @yetkinyilmaz this is something you requested to watch as well.
You can sign-off by replying to this message having '+1' in the first line of your reply.
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@Degano you are the release manager for this.
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[slava77]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

+1
Tested at: b702018
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-11223/7995/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-11223/7995/summary.html

[cvuosalo]

+1

For #11223 b702018

For Heavy Ions, adding E/p cut to electrons.

The code changes are satisfactory, and Jenkins tests against baseline CMSSW_7_6_X_2015-09-09-2300 show no significant differences. An extended test with 70 events of workflow 140.53_RunHI2011 against baseline CMSSW_7_6_0_pre4 also shows no significant differences. CPU timing and product sizes also did not change significantly.

[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