[#56904820] added inherited model level validations to cms

Used before_validation callback to run inherited model level validations on the CMS. I couldn't think of how to validate without using the callback as I needed to get the attribute "_type" in order to figure out which validations to run. Felt a bit 'dirty' because the inherited models weren't in the CMS and the validations depended on their type, so please let me know if these should live elsewhere.