Chess: Capitalize chess set names + Rename 'stelar7' to 'Classic'

Now when selecting a chess set in Games Settings, the names of the sets
are capitalized which looks much neater.

The default set 'stelar7' has been renamed to 'Classic' to reflect its
default vanilla design, as opposed to more stylized sets.
This commit also updates any code references to this set.

Userland/Applications/GamesSettings/ChessSettingsWidget.cpp

@@ -239,7 +239,7 @@ ErrorOr<void> ChessSettingsWidget::initialize()
 {
     TRY(load_from_gml(chess_settings_widget_gml));
 
-    auto piece_set_name = Config::read_string("Games"sv, "Chess"sv, "PieceSet"sv, "stelar7"sv);
+    auto piece_set_name = Config::read_string("Games"sv, "Chess"sv, "PieceSet"sv, "Classic"sv);
     auto board_theme = get_board_theme(Config::read_string("Games"sv, "Chess"sv, "BoardTheme"sv, "Beige"sv));
     auto show_coordinates = Config::read_bool("Games"sv, "Chess"sv, "ShowCoordinates"sv, true);
 
@@ -302,8 +302,8 @@ void ChessSettingsWidget::reset_default_values()
 {
     // FIXME: `set_text()` on a combobox doesn't trigger the `on_change` callback, but it probably should!
     //        Until then, we have to manually tell the preview to update.
-    m_piece_set_combobox->set_text("stelar7");
-    (void)m_preview->set_piece_set_name("stelar7");
+    m_piece_set_combobox->set_text("Classic");
+    (void)m_preview->set_piece_set_name("Classic");
     auto& board_theme = get_board_theme("Beige"sv);
     m_board_theme_combobox->set_text(board_theme.name);
     m_preview->set_dark_square_color(board_theme.dark_square_color);

Userland/Games/Chess/ChessWidget.cpp

@@ -23,7 +23,7 @@
 ErrorOr<NonnullRefPtr<ChessWidget>> ChessWidget::try_create()
 {
     auto widget = TRY(AK::adopt_nonnull_ref_or_enomem(new (nothrow) ChessWidget));
-    widget->set_piece_set("stelar7"sv);
+    widget->set_piece_set("Classic"sv);
 
     return widget;
 }

Userland/Games/Chess/main.cpp

@@ -83,7 +83,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
 
     window->set_icon(app_icon.bitmap_for_size(16));
 
-    widget->set_piece_set(Config::read_string("Games"sv, "Chess"sv, "PieceSet"sv, "stelar7"sv));
+    widget->set_piece_set(Config::read_string("Games"sv, "Chess"sv, "PieceSet"sv, "Classic"sv));
     widget->set_board_theme(Config::read_string("Games"sv, "Chess"sv, "BoardTheme"sv, "Beige"sv));
     widget->set_coordinates(Config::read_bool("Games"sv, "Chess"sv, "ShowCoordinates"sv, true));
     widget->set_show_available_moves(Config::read_bool("Games"sv, "Chess"sv, "ShowAvailableMoves"sv, true));