Add support for JSONP and CORS in the Python REST interface

This change allows web browser applications to retrieve atom space data from a CogServer, via the Python REST interface, even if the server is running on a different host or port. For browsers that recognize the Cross Origin Resource Sharing (CORS) headers, data can be retrieved using XMLHttpRequest; for browsers that don't support CORS, there is a JSONP option, which pads the JSON data in a JavaScript function call.