Raffle winners who have accepted their spot will have to register an account,
which automatically forms a team with the user as leader. These accounts are saved
and identified by the event user model, for example the RiverRaftingUser in the case
of the River Rafting instance of the registration system.
Accounts (i.e users) are identified by their person number/SSN (sv. personnummer). Users also have other
properties depending on each event; as an example, the RiverRaftingUser has properties
describing if they want to buy lifevests and helmets or not.
To extend and include more properties, each event should edit their own user model,
found in models/<event> instead of editing the base user model.