Defines a callback for the notifications permission

[dominikweifieg]

When using frameworks like PushWoosh or OneSignal, the app has to call methods on these frameworks to request the permission for notifications from iOS. Since PermissionScope calls UIApplication.shared.registerUserNotificationSettings itself, it is not possible to use PermissionScope and, e.g., OneSignal together in an integrated way. I have added a notificationRequestCallback which, if set, will be called instead of UIApplication.shared.registerUserNotificationSettings in requestNotifications

[nickoneill]

Thanks @dominikweifieg, this sounds reasonable. Can you add this to the docs as well?

[dominikweifieg]

Sure, will do so tomorrow morning my time and add it to the pull request. Thanks!