private void addStockToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Search_Stock_Prices ssp = new Search_Stock_Prices(ref mainPortfolio);
            ssp.ShowDialog();

            mainPortfolio = ssp.ThisPortfolio;

            UpdateGraph();
        }
        private void searchStocksToolStripMenuItem_Click(object sender, System.EventArgs e)
        {
            Search_Stock_Prices ssp = new Search_Stock_Prices(ref thisPortfolio);
            ssp.ShowDialog();

            thisPortfolio = ssp.ThisPortfolio;

            UpdateGraph();
        }