Show previous answers to registration fields when updating registrations
Closes #56
Previous behaviour
When updating a registration in the app, like the Thalia weekend, all fields are blank.
Steps to reproduce:
- Register for an event with fields
- Enter values for these fields
- Save your registration
- Edit your registration
- Notice all fields are blank
New behaviour
When updating a registration in the app, your previous answers are shown.
Steps to validate that it works:
- Register for an event with fields
- Enter values for these fields
- Save your registration
- Edit your registration
- Notice it shows your previous answers.