Okay some ideas:

We want a modular system.
A signup form = list of signup questions
A signup = list of signup answers


Examples of questions:
* Dietary restrictions
* Insurance info
* Pick option from list
* Team (interesting one, as people can also make new teams)


class SignupQuestion
--> SignupQuestionDiet, SignupQuestionInsurance, SignupQuestionOption ....
Questions differentiate through enum question_type
Questions can have parameters like Option

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Every SignupQuestionXYZ has a SignupAnswerXYZ


An activity consists of:
* usual event stuff, email, max_attendees, ....
* a slug!
* dict of SignupQuestions
* list of QuestionOrder

A signup then consists of:
* ActivityRef (what activity)
* EntityRef (who signed up)
* optional payment_id
* optional is_reserve
* optional confirmed (true if paid)
* dict of SignupAnswers

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When saving a signup, we check:
* get activity
* is person allowed to sign up?
* do we have enough signup answers
* for every answer: does answer validate type of question?