refs https://github.com/TryGhost/Ghost/pull/12736
refs https://github.com/TryGhost/Team/issues/467
knex's `parse()` method is only called on data when directly fetched from the db. This was causing problems when model instances are passed around via events for example because `.get('key')` will return data that was directly set on the model without having gone through the `parse()` transformations. The result of this inconsistency was settings appearing correct when Ghost started up but then being broken as soon as a setting was changed.
- moved absolute/relative->transform-ready URL transformations from the API input serializers to the model's `format()` method and replaced with a relative->absolute transform in API input serializers
- results in consistency because `.get()` on a settings model will always return an URL
- removed transform-ready->absolute transforms from the API output serializers as that is now handled at the model-layer