Add an option for shifts to be "required" : if they are not filled X days before, specific accounts get notified.

[Theophile-Madet]

For each shift, we should be able to specify how many days before the warnings goes out (maybe in hours? or "at 18:00 the day before"?) and to which accounts the mail gets sent to. The email address linked to those accounts should be used.

[crosspolar]

[crosspolar]

Tests TODO

• Every User can register to a ShiftWatch of a shift only once
• Shift is deleted from ShiftWatch too when shift has been cancelled

[Theophile-Madet]

@crosspolar do you have any work in progress on this? The PR is closed but I'm not sure if there's anything to keep from it?

[crosspolar]

I found the requirement engineering a bit overwhelming, as you can see in the PR. I decided, that being able to choose which kind of mails to receive is obligatory for this, so I started programming this. The WIP is the PR itself basically, but I wasn't happy with the design.

[crosspolar]

If you need a very basic method to notify just one mail adress with a fixed time ahead, it can be done much easier. But the PR aimed at members being able to "watch" shifts and get notified if the shift is understaffed.