Widgetsignatue

Process signature file in widget according to http://www.w3.org/TR/widgets-digsig/#signature-verification. Because there is no Tizen CA root in image, reference validation and signature validation on signature will be added when CA is ready.
 LogErrorLibxml2() and LogWarningLibxml2() are as parameters for function 	xmlSchemaSetValidErrors in http://xmlsoft.org/html/libxml-xmlschemas.html#xmlSchemaValidityErrorFunc. Unless we don't output error message, I think we have to use required API format. And I have implemented the log function using LOG().