private void verGestionesToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Form existe = Application.OpenForms.OfType <Form>().Where(pre => pre.Name.Contains("FormGestionesPrincipal")).SingleOrDefault <Form>();

            if (existe != null)
            {
                existe.WindowState = FormWindowState.Maximized;
                existe.BringToFront();
            }
            else
            {
                Presentacion.Tareas.FormGestionesPrincipal newMDIChild = new Presentacion.Tareas.FormGestionesPrincipal();
                newMDIChild.MdiParent   = this;
                newMDIChild.WindowState = FormWindowState.Maximized;
                newMDIChild.Show();
            }
        }