message: Move `FactoryListBox` globals into unnamed namespace
diff: using namespace NAS2D;
  +namespace
  +{
  const int LIST_ITEM_HEIGHT = 58;
  const Image* STRUCTURE_ICONS = nullptr;
  static const Font* MAIN_FONT = nullptr;
  static const Font* MAIN_FONT_BOLD = nullptr;
  +}
  static void drawItem(Renderer& renderer, FactoryListBox::FactoryListBoxItem& item, int x, int y, int w, int offset, bool highlight)
  