Clean up of sandbox

* Added a statistics panel
* Added comments to `Sandbox.cpp`
* Moved utility functions and GUI code out of sandbox.cpp

BarinkEngine/Include/BarinkEngine.h

@@ -16,6 +16,6 @@
 #include "Graphics/GUI/GUIManager.h"
 #include "Scene.h"
 
-void WARN(std::string message);
 
 
+void ShowStats();