/// <summary>
        /// Loads all difficulties.
        /// </summary>
        public void LoadDifficulties()
        {
            tableLayoutPanelDifficulties.ColumnCount = 0;

            ExerciceDifficulty[] difficulties = (ExerciceDifficulty[])Enum.GetValues(typeof(ExerciceDifficulty));
            for (int i = 0; i < difficulties.Length; i++)
            {
                ExerciceDifficulty difficulty = difficulties[i];

                Button button = new Button();
                button.Text         = ExerciceForm.GetLangString(difficulty.ToString());
                button.Height       = 40;
                button.Anchor       = AnchorStyles.None;
                button.TabIndex     = i;
                button.DialogResult = DialogResult.OK;
                button.Click       += (sender, e) =>
                {
                    SelectedDifficulty = difficulty;
                };
                tableLayoutPanelDifficulties.ColumnCount++;
                tableLayoutPanelDifficulties.ColumnStyles.Add(new ColumnStyle(SizeType.Percent, 100.0F));
                tableLayoutPanelDifficulties.Controls.Add(button, tableLayoutPanelDifficulties.ColumnCount - 1, 0);
            }
        }