Add UI setting for whether programmable signals shown in UI (default off)

Add setting subcategory for advanced signal features

src/settings.cpp

@@ -1062,6 +1062,13 @@ static bool DragSignalsDensityChanged(int32)
 	return true;
 }
 
+static bool ProgrammableSignalsShownChanged(int32)
+{
+	InvalidateWindowData(WC_BUILD_SIGNAL, 0);
+
+	return true;
+}
+
 static bool TownFoundingChanged(int32 p1)
 {
 	if (_game_mode != GM_EDITOR && _settings_game.economy.found_town == TF_FORBIDDEN) {