Add progress handler to uploadContent

bluebird doesn't support promise progression (or rather, it does, but it's
heavily deprecated and doesn't use the same API as q), so replace the
(undocumented) promise progression on uploadFile with a callback.

src/http-api.js

@@ -134,6 +134,10 @@ module.exports.MatrixHttpApi.prototype = {
      *    invoke on success/failure. See the promise return values for more
      *    information.
      *
+     * @param {Function=} opts.progressHandler Optional. Called when a chunk of
+     *    data has been uploaded, with an object containing the fields `loaded`
+     *    (number of bytes transferred) and `total` (total size, if known).
+     *
      * @return {module:client.Promise} Resolves to response object, as
      *    determined by this.opts.onlyData, opts.rawResponse, and
      *    opts.onlyContentUri.  Rejects with an error (usually a MatrixError).
@@ -260,7 +264,12 @@ module.exports.MatrixHttpApi.prototype = {
                 upload.loaded = ev.loaded;
                 upload.total = ev.total;
                 xhr.timeout_timer = callbacks.setTimeout(timeout_fn, 30000);
-                defer.notify(ev);
+                if (opts.progressHandler) {
+                    opts.progressHandler({
+                        loaded: ev.loaded,
+                        total: ev.total,
+                    });
+                }
             });
             let url = this.opts.baseUrl + "/_matrix/media/v1/upload";
             url += "?access_token=" + encodeURIComponent(this.opts.accessToken);