More fixes/tweaks to the installer

- Add Windows icon for scenario files (using the old Mac icon)
- Fix OpenAL not being deleted, causing the program directory to remain
- Fix association for old scenarios (.exs) not being removed
Also:
- Fix build broken in previous commit (due to header renames)

src/pcedit/pc.menus.win.cpp

@@ -2,7 +2,7 @@
 #include "pc.menus.hpp"
 #include <map>
 #include <SFML/Graphics/RenderWindow.hpp>
-#include "Resource.h"
+#include "pcresource.h"
 #include "universe.hpp"
 #include "winutil.hpp"
 #include "menu_accel.win.hpp"