message: Use constructor init list for control text in GameOverDialog
diff: using namespace NAS2D;
  -GameOverDialog::GameOverDialog() : mHeader("ui/interface/game_over.png")
  +GameOverDialog::GameOverDialog() :
  + mHeader{"ui/interface/game_over.png"},
  + btnClose{"Return to Main Menu"}
  {
  init();
  }
  @@ -28,7 +30,6 @@ void GameOverDialog::init()
  size(522, 340);
  add(&btnClose, 5, 310);
  - btnClose.text("Return to Main Menu");
  btnClose.size(512, 25);
  btnClose.click().connect(this, &GameOverDialog::btnCloseClicked);
  