Support changelog / canteen update notification

[mswart]

For other tools I would be very helpful, if they could be subscribe to canteen changes (new canteen, canteen updated ...) - either on human basis (E-Mail to user) or software basis (API call ...).

In addition I think it would make sense to create a changelog/news page, where users can see the last changes for canteens (new canteens, updated canteens ...)