Team application configuration restructure

Currently the "apply as a team" functionality is controlled by enabling or disabling the "Do you want to apply as a team?" question under the registration form settings.

Instead, this should be configurable in a section under the Configuration tab in the event admin panel. The following should be configurable:

- What is the maximum team size? (defaults to 5)
- Can participants apply as a team? (yes/no)

If the answer to the second question is yes, show a Team section in the registration form which asks the user if:

a) They are applying as a team, and b) If they want to also apply individually should their team not get accepted