Support DateTimeOffset in wsdl generation

[nalla]

Currently, when using DateTimeOffset as type an error is thrown indicating that the type is not supported.

.NET type DateTimeOffset cannot be resolved into XML schema type

Instead something similar to here should be constructed.

<xs:schema targetNamespace="http://schemas.datacontract.org/2004/07/System">  
   <xs:complexType name="DateTimeOffset">  
      <xs:sequence minOccurs="1" maxOccurs="1">  
         <xs:element name="DateTime" type="xs:dateTime"  
         minOccurs="1" maxOccurs="1" />  
         <xs:elementname="OffsetMinutes" type="xs:short"  
         minOccurs="1" maxOccurs="1" />  
      </xs:sequence>  
   </xs:complexType>  
</xs:schema>

[drabb1956]

WSDL generation is failing for me when a parameter or property is Nullable of DateTimeOffset