Create a function like get_key_fields_for_object_type, but for required fields

[blthayer]

To create new objects in a model you need both the key fields and the required fields.

This should be as simple as making a helper function which is nearly identical to get_key_fields_for_object_type, but takes regular expressions as input. Then, get_key_fields_for_object_type would call this helper function, and a new function, get_required_fields_for_object_type would also call it.