Got the PUT roundtrip for `/circle/` working.

* [QR_OBJECTS,EXT] Use HTTP PUT method for sending the user-given label of a circle.
* [QR_OBJECTS,EXT] Add JSON content type to HTTP request.
* [WEBQR,SC] Use the new www_browser-based xml prefix registration routine. This allows us to register URLs in a more organized way (as with file_search_path).
* [WEBQR_SERVER,EXT] Execute the HTTP PUT method for path `/circle/`.