Notifications for RSVP changes within <x> hours / days before an training / match#281

People are able to change their RSVP to an calendar item (training / match / event) but if they change something you don’t get any notification. It would be nice if you can setup a notification if a change in RSVP is done within <x> hours / days before a match or a triaining. This way a cancellation don’t needs a seperate message but is directly visible for staff from within the app.