Properly handle long lists of Parameters

[davidlange6]

Changed the code so that if we have more than 200 Parameters in a __Parametrizable object we switch to filling a dict using lists of no longer than 200 entries where the lists are concatenated together to build a container holding all the Parameters.

backport of 10333

[cmsbuild]

A new Pull Request was created by @davidlange6 (David Lange) for CMSSW_7_5_X.

Properly handle long lists of Parameters

It involves the following packages:

FWCore/ParameterSet

@cmsbuild, @smuzaffar, @Dr15Jones can you please review it and eventually sign? Thanks.
@Martin-Grunewald, @wddgit, @wmtan 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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[Dr15Jones]

@davidlange6 thanks!