for handling base64
- Added xmlbeans dep for validating XML, esp. anyURI as java.net.URI not
compliant with XSD anyURI type
- removed uses of java.net.URI for attribute datatype since not
compliant with XSD anyURI
- Fixed BUG when no subject and resource and action attributes in
request
- Use of parameter types 
- Changed AttributeProxy interface and implementations (added a
AbstractPrimitiveAttributeProxy class for primitive types) to allow for
Structure attribute datatypes such as XML node/JAXBElements