Add a hidden preference to skip the Spiderweb logo at startup

The same preference also skips the scenario editor startup splash
In order to enable that, the scenario editor now loads prefs.

src/game/boe.main.cpp

@@ -178,6 +178,10 @@ void init_boe(int argc, char* argv[]) {
 	init_startup();
 	flushingInput = true;
 	show_logo();
+	// Hidden preference to hide the startup logo - should be kept hidden
+	if(get_bool_pref("ShowStartupLogo", true))
+		show_logo();
+	// The preference to hide the startup splash is exposed however.
 	if(get_bool_pref("ShowStartupSplash", true))
 		plop_fancy_startup();