AtomPub: createDocument() doesn't transmit the filename

The CMIS specification doesn't define how the filename of the content stream should be transmitted when a document is created. Therefore, OpenCMIS doesn't include it in the request.

The spec defines an extension point in cmisContentType, which could be used to add the filename. We should add an OpenCMIS extension, so that at least an OpenCMIS client (and maybe other clients) can send the filename to an OpenCMIS server.