Improve vertex validation

[rovere]

This PR will fix an offset-by-one bug that was present in the old version while computing mistag and add a rather comprehensive documentation on how to run and use this validation package.

Further code improvements, mainly related to logic and speed, have been included.

[cmsbuild]

A new Pull Request was created by @rovere (Marco Rovere) for CMSSW_7_2_X.

Improve vertex validation

It involves the following packages:

Validation/RecoVertex

@ojeda, @danduggan, @rovere, @cmsbuild, @nclopezo, @deguio, @Degano can you please review it and eventually sign? Thanks.
@cerati, @venturia, @GiacomoSguazzoni, @VinInn 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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[deguio]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_2_X IBs unless changes or unless it breaks tests.

[cmsbuild]

+1
Tested at: 09c92cd
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-4775/474/summary.html

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_2_X IBs unless changes (tests are also fine).

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-4775/474/summary.html