Extended AJAX JSON support and optional vaolue encode

Added the contentType ajax option defaults to 'application/x-www-form-urlencoded' can be changed to 'application/json; charset=utf-8' which is required for .net web service support. To support this
this the response must check data.d not just data - this has been added so both responses are supported..

Also to support the use of a URL (or other non encode required values) as the returned value the
encodeURIComponent in the buildItems function must be able disabled, so the new option encodeValue was added this defaults to true which means the value is encoded - set to false to support URL or non encode required values.