/// <summary>
/// Delete existing grade
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void DeleteGrade_Click(object sender, RoutedEventArgs e)
{
long id = _gradesDictionary[_selectedGrade.Name];
_contentManager.DeleteGrade(id, _educationalLevelDictionary[_selectedEducationalLevel.Name]);
_gradesDictionary.Remove(_selectedGrade.Name);
WrapPanelGrades.Children.Remove(_selectedGrade);
_selectedGrade = null;
EditGrade.IsEnabled = false;
DeleteGrade.IsEnabled = false;
NoOfFiles.Text = "";
NoOfLessons.Text = "";
NoOfWeeks.Text = "";
EditWeeks.IsEnabled = false;
EditLessons.IsEnabled = false;
EditFiles.IsEnabled = false;
}
