public void AddTravellerAsPresent(Traveller traveller)
{
traveller.SetAsPresent();
}
public void AddTraveller(Traveller traveller)
{
traveller.RegistrationDate = DateTimeOffset.Now;
traveller.Name = traveller.firstname + " " + traveller.lastname;
Travellers.Add(traveller);
UpdateAcceptingMoreSignUps();
}