* First pass at adding feature flags. Accessible over PHP and JS.
* Hook up dev config to test enviornments, hook up features to their flags.
* Cleanup some code and add documentation. Remove beta config.
* Handle PR Feedback: Add devdocs flag, remove categories flag, fix auto-generated PHP warning.
* Add todo for beta phase.
* Handle PR feedback: Simplify is_array check, update build command, simplify test mock, remove empty webpack line.
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