Cancellation status messages for registrations

[rodepanda7]

Closes #398 .

Summary

There was a small bug in the logic of displaying the correct registration info
If you cancel your registration, you won't be registered for the event anymore. I changed an or to an and. If we keep the 'or', the following message will be displayed if you cancelled your registration after the deadline, instead of the message we would like to display: 'Registration is not possible anymore. '

I also added the field registrationStatus to Event, so we can display the same message as the website

How to test

1. Go to the event mooi test event
2. Register for the event
3. Change registration deadline
4. Deregister for the event and you should get the message in the app: "Your registration is cancelled after the deadline and you will pay a fine of €10,00."

[JAicewizard]

Can you undo the changes to pubspec?

[JAicewizard]

@rodepanda7

[JAicewizard]

It has been a while, are you going to be at technicie next week? Maybe explain the changes to me again, and then I can maybe explain how to make tests. (The logic behind the event message is quite complicated, a test might be a good idea in general)

The merge-base changed after approval.