Enrich simple type detection

[tefra]

Currently the class analyzer considers all not xs:element or xs:complexType as simple types. This excludes elements with anySimpleType and complex types with simple content.

<xs:schema>
  <xs:element name="x" type="xs:string"

[tefra]

One assumption I want to try is that any class with a single text field is a simple type, for both attributes and class extensions