Refs #689 - Emit an event after fireInitial

Add a `values-loaded` event fired on local backend after all values have been loaded.

Sample usage:

     remoteStorage.on("features-loaded", function (e) {
       remoteStorage.local.on('values-loaded', function onValuesLoaded(ev) {
         console.log("All items loaded at " + window.performance.now());
       });
     });