Notification handler

Now it is clearer how notifications are handled in the activity and how you can add a custom handler to do it your way.

The app developer can use one of these methods in the activity:

    MalcomLib.checkNotification(this);
    MalcomLib.checkNotification(this, handler);

https://github.com/MyMalcom/malcom-lib-android/blob/a524b03dfdeeacd42806a0099bc1ab95ce54ac55/doc/Notifications.md#check-notification