Created the loadGameMap() function, still incomplete

Although the overall logic of this function is finished, I still need to
write the callbacks for RegionPager's onNew and onDelete.

I've also tested this using a hand written save/index file. I've written
up a map file format by hand, and I'll be implementing it over the next
few commits.

editor/editor_scene.hpp

@@ -31,6 +31,8 @@
 #include "raster_font.hpp"
 #include "menu_bar.hpp"
 
+#include "map_loader.hpp"
+
 #include <list>
 
 class EditorScene : public BaseScene {