Stabilize support for custom profile fields.

[clokep]

Implements stable support for arbitrary profile fields but essentially switching the implementation to the previous experimental version.

This maintains backward plasticity with the experimental feature as a transitional measure, but updates the tests to test the stable paths.

Pull Request Checklist

• Pull request is based on the develop branch
• Pull request includes a changelog file. The entry should:
  • Be a short description of your change which makes sense to users. "Fixed a bug that prevented receiving messages from other servers." instead of "Moved X method from EventStore to EventWorkerStore.".
  • Use markdown where necessary, mostly for code blocks.
  • End with either a period (.) or an exclamation mark (!).
  • Start with a capital letter.
  • Feel free to credit yourself, by adding a sentence "Contributed by @github_username." or "Contributed by [Your Name]." to the end of the entry.
• Code style is correct (run the linters)

[anoadragon453]

Looks good on the whole! Just a couple question below.

Thank you for doing this!

[clokep]

Thanks @anoadragon453, should be ready for another look.

[anoadragon453]

LGTM. Thank you!