Pseudo-stream version of JSON monitoring for 73X

[avetisya]

This is an exact copy of PR#6095 intended to port the latter to 73X. The description of the original PR is copied below.

This update to HLTrigger/JSONMonitoring switches to the pseudo-stream version and also adds some Level 1 trigger rate information. It requires the toJsonValue() function and thus also pulls in Srecko's changes to EventFilter/Utilities/interface/JsonMonitorable.h per his suggestion.

[cmsbuild]

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

Pseudo-stream version of JSON monitoring for 73X

It involves the following packages:

EventFilter/Utilities
HLTrigger/JSONMonitoring

@perrotta, @cmsbuild, @nclopezo, @emeschi, @Martin-Grunewald, @fwyzard, @mommsen can you please review it and eventually sign? Thanks.
You can sign-off by replying to this message having '+1' in the first line of your reply.
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@nclopezo, @ktf you are the release manager for this.
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[Martin-Grunewald]

+1

[cmsbuild]

+1
Tested at: 230379d
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-6105/517/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-6105/632/summary.html

[Martin-Grunewald]

+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 will be automatically merged.