Preload settings callbacks

[davideast]

Add settings to preload callbacks

This PR adds settings callbacks to all preload methods:

preloadDatabase(app, db => db().goOffline());
preloadAuth(app, auth => auth()...);
preloadAnalytics(app, analytics => analytics()...);
preloadFirestore(app, firestore => firestore().enablePersistence());
preloadFunctions(app, functions => functions()...);
preloadMessaging(app, messaging => messaging()...);
preloadPerformance(app, performance => performance()...);
preloadRemoteConfig(app, remoteConfig => {
   remoteConfig.settings = { }
   return remoteConfig().fetchAndActivate();
});
preloadStorage(app, storage => storage().setMaxUploadRetryTime(10000));

closes #203

[jhuleatt]

Looks great! A todo for the future is to remove initPerformance from FirebaseAppProvider now that it's easy to initialize it like all the other SDKs