Fix event registration terms URL in event page

Closes #941 (closed)

Previous behaviour

The link to the terms and conditions of event registrations is broken.

Steps to reproduce:

1. Open an event with open registration.
2. Press the link to the terms and conditions.
3. Notice you are directed to the same page.

New behaviour

The link to the terms and conditions of event registrations points to the correct page.

Steps to validate that it works:

1. Open an event with open registration.
2. Press the link to the terms and conditions.
3. Notice you are directed to the terms and conditions page.