Stop storing preferences and legacy flags in the saved game

- Nuke global preference variables (they're now fetched with get_xxx_pref whenever needed)
- Nuke magic SDFs that store preferences and other info
- The only preferences now stored in the saved game are those related to difficulty
- play_sound no longer takes an option repeat parameter, but instead takes a delay which will be used if sounds are disabled
- SDF array increased to 350x50
- When saving a legacy scenario, a dialog is shown to remind you to update and to allow you to clear the legacy flag

src/scenedit/scen.fileio.cpp

@@ -19,6 +19,7 @@
 #include "tinyprint.h"
 #include "map_parse.hpp"
 #include "winutil.hpp"
+#include "choicedlog.hpp"
 
 #define	DONE_BUTTON_ITEM	1
 
@@ -960,6 +961,9 @@ void save_scenario(bool rename) {
 		if(toFile.empty()) return;
 	}
 	
+	if(scenario.is_legacy && cChoiceDlog("save-legacy-scen", {"update", "cancel"}).show() == "update")
+		scenario.is_legacy = false;
+	
 	scenario.reset_version();
 	tarball scen_file;
 	{