private void btnNeemTerug_Click(object sender, EventArgs e)
        {
            ObjectReservation res = (ObjectReservation)listBox2.SelectedItem;

            _vc.TakeBack(res);
            listBox1.DataSource = null;
            listBox2.DataSource = null;
            listBox1.DataSource = _vc.GetReserved();
            listBox2.DataSource = _vc.GetBorrowed();
        }
        private void btnGeefUit_Click(object sender, EventArgs e)
        {
            ObjectReservation res = (ObjectReservation)listBox1.SelectedItem;

            _vc.Borrow(res);
            listBox1.DataSource = null;
            listBox2.DataSource = null;
            listBox1.DataSource = _vc.GetReserved();
            listBox2.DataSource = _vc.GetBorrowed();
        }