De-C++-ify struct ScreenSettings

This includes:
- Removing the constructor in favor of actually being able to see that
  there's an actual function called being made initializing the struct
- Removing the use of a reference in Screen::init() in favor of using a
  pointer
- Adding the struct qualifier everywhere (it's not much typing),
  although technically you could typedef it in C, but I'd rather much
  not typedef just to remove a tag qualifier

desktop_version/src/ScreenSettings.h

@@ -3,8 +3,6 @@
 
 struct ScreenSettings
 {
-    ScreenSettings(void);
-
     int windowWidth;
     int windowHeight;
     bool fullscreen;
@@ -14,4 +12,6 @@ struct ScreenSettings
     bool badSignal;
 };
 
+void ScreenSettings_default(struct ScreenSettings* _this);
+
 #endif /* SCREENSETTINGS_H */