Allow SoftKiller to run on packed candidates

[ahinzmann]

Backport of #7649
SoftKiller is a general pileup removal algorithm.
This pull request enables using packedCandidates instead of PFCandidates as input, such that it can be run on MiniAOD.
The same strategy to handle both inputs as in the PUPPI pileup algorithm is used.

[cmsbuild]

A new Pull Request was created by @ahinzmann for CMSSW_7_3_X.

Allow SoftKiller to run on packed candidates

It involves the following packages:

CommonTools/PileupAlgos

@nclopezo, @cvuosalo, @monttj, @cmsbuild, @slava77, @vadler can you please review it and eventually sign? Thanks.
@rappoccio this is something you requested to watch as well.
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@nclopezo 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: df6ee3b
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-7667/2516/summary.html

[ahinzmann]

yes, it is linked in the description: #7649

[monttj]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_3_X IBs unless changes (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @nclopezo, @ktf, @smuzaffar

[davidlange6]

+1