[RTM] Add the Amazon SWS XML Namespace to the XML data returned by the responder

The AWS SDK for .NET requires that the elements returned by the SQS service include the "http://queue.amazonaws.com/doc/2012-11-05/" namespace in order to be correctly de-serialized. I added an option that allows the namespace to be set to the provided value. If no value is provided, the namespace is set to the default AWS namespace.

NOTE: I was unable to get the tests to run on my Windows development box.

@dhoizner @dvishnepolsky @tmartino-mdsol Please review.