Chess: Change default piece set

As much as I like the "test" piece set, I think "stelar7" is a much
better first impression for anyone opening the Chess game, so I
consider it a much more sensible default.

Games/Chess/ChessWidget.cpp

@@ -37,7 +37,7 @@ ChessWidget::ChessWidget(const StringView& set)
 }
 
 ChessWidget::ChessWidget()
-    : ChessWidget("test")
+    : ChessWidget("stelar7")
 {
 }
 

Games/Chess/main.cpp

@@ -78,7 +78,7 @@ int main(int argc, char** argv)
 
     window->set_icon(app_icon.bitmap_for_size(16));
 
-    widget.set_piece_set(config->read_entry("Style", "PieceSet", "test"));
+    widget.set_piece_set(config->read_entry("Style", "PieceSet", "stelar7"));
     widget.set_board_theme(config->read_entry("Style", "BoardTheme", "Beige"));
     widget.set_coordinates(config->read_bool_entry("Style", "Coordinates", true));