static addEventListener(type, handler)
Attaches a listener to remote or local notification events while the app is running in the foreground or the background.
Valid events are:
notification : Fired when a remote notification is received. The handler will be invoked with an instance of PushNotificationIOS.
localNotification : Fired when a local notification is received. The handler will be invoked with an instance of PushNotificationIOS.
register: Fired when the user registers for remote