As a Developer I want $contentType->contentTypeGroups to be loaded lazily since I usually don't need to iterate on them, I mainly need to get info on the type only and don't want to see it slowed down by group loading and object mapping.

This is to be served as example of how to enrich the API with more lazy loaded properties.

Implementation note: This can be done using Generator available in PHP 5.5 and higher. Besides saving on unneeded loads, doing this kind of changes several places on the api should theoretically have the benefit of reducing memory consumption.