Set categories for properties that are not top-level

[kiendang]

With the current implementation categories are only enforced for top-level properties. However sometimes we may want to be able to set categories for lower level fields.

For example,

user:
  categories:
    - unrestricted
  properties:
    name:
      categories:
        - personally-identifiable-information
    admin:

Here user is a top-level property however we may only want to tag the username name as personally identifiable information.