Add Penalty Protection (PrikkSkjold™️)

[AdrianAndersen]

Automatically unregister the user before the deadline, unless the user has explicitly confirmed the class.

There are two ways to use PrikkSkjold™️ for a class/classes

PrikkSkjold™️

The user can flip a toggle in sit-rezervo-confgen for each class. Eg. Enable PrikkSkold™️
Then, when sit-rezervo books the class, there is a "Confirm Class" button on the Slack message sit-rezervo sends.

• If the user does not press the button before the unregister deadline, sit-rezervo automatically unregisters the user, and marks the class as unregistered, with PrikkSkjold™️ as the reason. (+ tags the user)
• If the users does press the button, the class is confirmed, the button disappears, and the class is kept as normal. Nice to send a message to the user in thread to confirm that the class is "locked in"
• At a certain offset before the deadline eg. two hours before the deadline, the sit-rezervo sends a message to the user in the thread for the class, reminding them that they need to confirm the class, to avoid it being unregistered.

AutoPrikkSkjold™️

A global toggle in sit-rezervo-confgen, where the user can enable AutoPrikkSkjold™️.
This feature automatically enables PrikkSkjold™️ for all bookings when the user has two Penalties.

[mathiazom]

Will probably need some kind of persistance to store booking confirmations. Slack might provide bot storage, but I think we should go for a less Slack-dependant solution. Maybe it's time to try out Redis?