Game no longer frees the current stage

This is now up to the client. It makes more sense though; I found this
one when I created stages on the stack and the game tried to delete them
(oops).
Fixed Renderer::copy only accepting references

Passing NULL to SDL_RenderCopy instead of SDL_Rects is completely valid;
I just forgot :P. However, the new implementation could use some work.
Wrapped SDL_QueryTexture

Might implement individual get functions around it.