add NS_EWS_TYPES to SetItemField, Item and the build_xml methods to pass validation for creating a calendar item. This fixes validation error 'The element 'SetItemField' has invalid child element 'CalendarItem''. Change NS_EWS_MESSAGES to NS_EWS_TYPES for the FieldURI, IndexedFieldURI, and ExtendedFieldURI, the MSDN documentation has the validation type as Types.xsd.