Subject types are still hardcoded in some places, for example [here](https://github.com/WordPress/try-wordpress/blob/trunk/src/api/SubjectsApi.ts#L60) and [here](https://github.com/WordPress/try-wordpress/blob/trunk/src/model/Subject.ts#L4-L5). There should be no hardcoded values for subject types.
