Moved rendering helpers from structs/ to strucs/rendering

-Moved Particle.* and RenderingItem.* to strucs/rendering
-Updated Renderer.h to include the new headers
-Updated build/DXBall.pro with the moved .cpp file
Made more objects in const ref

-Changed most ( if not all ) autos into const auto &
-Hopefully this will improve performance and reduce the ammound of
copying of shared_ptr to a bare minimum