Properly order questions for event registrations

One-sentence description

The additional questions should be displayed in the desired order.

Current behaviour

Currently the symposium has a question wrt talk preference, but the rounds are not ordered increasingly (but seemingly randomly). However, in the back-end, the order fields are set properly.

Expected behaviour

The fields should be displayed in the prescribed order.

Steps to reproduce

1. Go to https://thalia.nu/admin/events/event/237/change/?next=/events/admin/237/
2. Observe that the order is as expected.
3. Go to https://thalia.nu/events/237/registration/ (assuming you've registered)
4. Observe that the order is disregarded.