Cancellations for today's booking

[dennmuel]

Allow cancellations of bookings by user and staff. Send a confirmation mail in both cases.

[stweil]

Cancellation is a standard function which already works. An e-mail can be sent optionally.

Admins can change (including) cancel any booking.

Please test and close this issue if everybody works well.

[dennmuel]

Seems to work. Does the email text make clear, that this change came form the staff?

[stweil]

There is a (lower priority) requirement to allow variable text elements for e-mails sent by master users.

[dennmuel]

Bookings for the current day cannot be cancelled after a certain hour, as some users noticed. Hence the title change. (Also the time up to which bookings are allowed could me made configurable.)