private void HallNewButton_Click(object sender, EventArgs e)
        {
            LectureHallForm form = new LectureHallForm();

            form.SetHall(new LectureHall());
            form.Show();

            form.FormClosed += LectureHallForm_Closed;
        }
        private void HallEditButton_Click(object sender, EventArgs e)
        {
            LectureHallForm form = new LectureHallForm();

            form.SetHall((LectureHall)HallCombobox.SelectedItem);
            form.Show();

            form.FormClosed += LectureHallForm_Closed;
        }