Slot_usage is not reflected in identifier class

[hsolbrig]

If you specialize the type of a class or slot name:

classes:
   schema_definition:
           is_a: element
           ...
          slot_usage:
            name:
                range: ncname

This is not reflected in the generated python:

class SchemaDefinitionName(ElementName):
    pass

It should be:

class SchemaDefinitionName(NCName):
    pass