I'd prefer to keep the application life cycle methods in `NCSNavFieldAppDelegate.m`.

How does this sound as an alternative proposal?

1. Add a method [ApplicationSettings registerForNSUserDefaultsDidChangeNotification] which is invoked in `NCSNavFieldAppDelegate#application:didFinishLaunchingWithOptions:`. This way the consumers that are listening for application settings updates don't have to be concerned with where we're storing our settings.
2. Add a method [ApplicationSettings announceSettingsChanged] that will send a notification when the applications settings are changed.
3. RootViewController's purge button toggle will listen for application settings change announcements.