public MainWindow()
{
InitializeComponent();
cbxUnionUser.ItemsSource = unionHandler.GetAllUnions();
dgActivitiesUser.ItemsSource = activityHandler.GetAllActivities();
cbxAdmin.ItemsSource = adminHandler.GetAllAdmins();
dgReservationsAdmin.ItemsSource = reservationHandler.GetAlllReservation();
dgBookingOverviewAdmin.ItemsSource = bookingHandler.GetAllBookings();
dgReservationsUser.ItemsSource = reservationHandler.GetAlllReservation();
}