private async void btnAdd_Click(object sender, EventArgs e)
        {
            ApplicationViewModel applicationViewModel = new ApplicationViewModel();
            await applicationViewModel.GetGrades(user.Login, user.Password);

            AddSubjectForm subjectsForm = new AddSubjectForm(user, applicationViewModel.handbookGrades, this);

            subjectsForm.Show();
        }
        private async void dataGridView_CellMouseDoubleClick(object sender, DataGridViewCellMouseEventArgs e)
        {
            string Name    = dataGridView.Rows[e.RowIndex].Cells["subjectName"].FormattedValue.ToString();
            string GradeId = dataGridView.Rows[e.RowIndex].Cells["Grade"].FormattedValue.ToString();
            string Id      = dataGridView.Rows[e.RowIndex].Cells["Id"].FormattedValue.ToString();
            ApplicationViewModel applicationViewModel = new ApplicationViewModel();
            await applicationViewModel.GetGrades(user.Login, user.Password);

            AddSubjectForm gradeForm = new AddSubjectForm(user, applicationViewModel.handbookGrades, this, Id, Name, GradeId);

            gradeForm.Show();
        }