private void btnCSBack_Click(object sender, EventArgs e)
        {
            OnBoard board = new OnBoard(plan);

            plan.Controls.Remove(this);
            plan.Controls.Add(board);
        }
        private void btnUserBack_Click(object sender, EventArgs e)
        {
            var onboard = new OnBoard(_plan);

            _plan.Controls.Add(onboard);
            _plan.Controls.Remove(this);
        }
        private void btnOnBoard_Click(object sender, EventArgs e)
        {
            OnBoard onboard = new OnBoard(plan);

            plan.Controls.Add(onboard);
            this.Visible = false;
        }