(js) New 'ready' method for Preferences service

This method returns a promise that succeeds when the user's defaults and
settings have been received from the server.

UI/WebServerResources/js/Preferences.app.js

@@ -82,7 +82,7 @@
    */
   statePreferences.$inject = ['Preferences'];
   function statePreferences(Preferences) {
-    return new Preferences();
+    return Preferences;
   }
   
 })();