Little tweaks and stuff

- New file extension .boes for scenarios - intent is to use this for the new scenario format
- Turn on auto-enable for Application menu in the game (otherwise the Show/Hide options don't grey out correctly)
- Fix PC graphics not appearing in PC editor

osx/pcedit/pc.graphics.cpp

@@ -242,6 +242,7 @@ void Set_up_win ()
 	status_gworld.loadFromImage(*ResMgr::get<ImageRsrc>("staticons"));
 	dlogpics_gworld.loadFromImage(*ResMgr::get<ImageRsrc>("dlogpics"));
 	buttons_gworld.loadFromImage(*ResMgr::get<ImageRsrc>("pcedbuttons"));
+	pc_gworld.loadFromImage(*ResMgr::get<ImageRsrc>("pcs"));
 }