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/Screen.h

@@ -8,10 +8,10 @@
 class Screen
 {
 public:
-    void init(const ScreenSettings& settings);
+    void init(const struct ScreenSettings* settings);
     void destroy(void);
 
-    void GetSettings(ScreenSettings* settings);
+    void GetSettings(struct ScreenSettings* settings);
 
     void LoadIcon(void);