'Change POU Type To' becomes 'Duplicate as...', avoiding side effects of type change when POU is already instanciated. Also remove leftover returType tag in ex-function POUs, triggering exceptions at build time.

                  <xsd:element name="Generic">
                    <xsd:complexType>
                      %(toolchain_makefile)s
                    </xsd:complexType>
                  </xsd:element>