Improve duplicate module filtering. Update SocketIO catch-all API.

[ryan-d-williams]

• Base your pull requests against the develop branch.
• Include these infos in the description:

• Does the pull request solve a related issue?
  Yes - solves Improvement to #3502 #3521

• If so, can you reference the issue like this Fixes #<issue_number>?
  Fixes Improvement to #3502 #3521 (also mentioned in commit message)

• What does the pull request accomplish? Use a list if needed.

• Updates duplicate module filter method (upstream vs downstream - see Multiple Instances of Node Helper running for a single module #3502)
• Updates socket io catchall functionality to new API [docs].

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• Don't forget to add an entry about your changes to the CHANGELOG.md file.