Cancel unconfirmed appointment

[benoiton]

If an appointment is requested but not confirmed, the slot is never released. Unconfirmed appointment should be automatically cancelled after some time (to be mentioned in confirmation mail). A reminder mail could be send before cancellation.

[SergeyMosin]

It is definitely a good idea, once I get the timing issues mentioned in https://github.com/SergeyMosin/Appointments/issues/68#issuecomment-655483744 figured out it will be easy to implement it.

[jpbraun]

This would be really a nice feature.