Add a notification when starting to save with the upload plugin

core/messages/StartingSave.tid

@@ -0,0 +1,3 @@
+title: $:/messages/StartingSave
+
+Starting to save wiki

core/modules/savers/upload.js

@@ -64,6 +64,7 @@ UploadSaver.prototype.save = function(text,callback) {
 		}
 	};
 	http.send(data);
+	$tw.notifier.display("$:/messages/StartingSave");
 	return true;
 };