Registers UI categories and moves default values from `config.set` blocks into schema `default` fields, so the configuration manager can drive everything directly from the schema. Only `actionButtons`, whose entries hold function bodies, stays in `config.set`.
Also adds a schema for `github.*` settings so the integration shows up in the configuration UI (later commit)
Refactor Library/Std into subfolders for APIs, Infrastructure, Editor,
Widgets, etc. Add more documentation and descriptions. Update references
throughout website and docs.
Zef Hemel