private void btn_addComment_Click(object sender, RoutedEventArgs e)
        {
            CommentWindow commentWindow = new CommentWindow();

            if (commentWindow.ShowDialog() == true)
            {
                taskContract.AddComment(commentWindow.CurrentText,
                                        (this.DataContext as Task).ID,
                                        GlobalSettings.CurrentUser.ID);
                UpdateComment((this.DataContext as Task).ID);
            }
        }