custom_registry.json customizes the wrong user account spec

[chisholm]

custom_registry.json has a customization for the User_Account spec; this is used in the jupyter notebook docs to demonstrate how one can customize generation. That customization is ignored because User_Account is simply a ref to user-account. The latter is what needs customizing. As it is, the generator sees the ref property and jumps to the target of the reference, ignoring anything else in the spec. So User_Account customizations, though they may be present, are never seen or used.