private void SearchPerson()
        {
            People.Clear();
            // Deze query kan beter! Hoe?
            var people = from p in personRepository.GetPeople()
                         where p.Firstname.ToLower().Contains(PersonName.ToLower()) || p.Lastname.ToLower().Contains(PersonName.ToLower())
                         select p;

            foreach (var p in people)
            {
                People.Add(p);
            }
        }