private void logout_btn_Click(object sender, EventArgs e)
        {
            InventoryMenu invM = ObjectHolder.inventoryMainMenu;

            this.Hide();
            invM.Show();
        }
 private void btnInventory_Click(object sender, EventArgs e)
 {
     if (invMenu == null)
     {
         invMenu = new InventoryMenu();
     }
     ObjectHolder.mainMenu = this;
     this.Hide();
     invMenu.Show();
 }