Allowed child types (file and image) on the Content container

[tusmester]

Currently Image is allowed on the /Root/Content container, but File isn't. This lets us upload documents in the root (or a subfolder) as images.

This is a snaas-only setting, the base product does not allow the Image type on the Content container.

Allow both the File and Image types on the Content container in the base packge and snaas too.