first commit of api spec

The content-store returns [`200` or `201`](https://github.com/alphagov/content-store/blob/master/app/controllers/content_items_controller.rb#L29), and we could pass that status back to the client. Since it considers `base_path` to be the primary key, though, it will return `201` whenever a new URL on GOV.UK is used for a court.

Instead, we could return `201` for a successful saving of a court with a new UUID, and 200 for a successful update. We already plan to track court UUIDs and the history of the slugs they use, so should have enough information in the API to do this.