* Document and support the established naming convention for config opts
This change:
* Rename `ConfigOptions` to `IConfigOptions` to match code convention/style, plus move it to a dedicated file
* Update comments and surrounding documentation
* Define every single documented option (from element-web's config.md)
* Enable a linter to enforce the convention
* Invent a translation layer for a different change to use
* No attempt to fix build errors from doing this (at this stage)
* Add demo of lint rule in action
* Fix all obvious instances of SdkConfig case conflicts
* Fix tests to use SdkConfig directly
* Add docs to make unset() calling safer
* Appease the linter
* Update documentation to match snake_case_config
* Fix more instances of square brackets off SdkConfig
This migrates one bucket of files using some amount of Flow typing to mark them
as TypeScript instead. The remaining type errors are fixed in subsequent
commits.
