Move all fixed-timestep render updates to new file RenderFixed.cpp

As part of fixing #464, I'll need to move these pieces of code around
easily. In #220 I just kind of shoved them awkwardly in whatever
fixed function would be last called in the gamestate loop, which I
shouldn't have done as I've now had to make formal fixed-render
functions anyway. Because these fixed functions need to be called
directly before a render function, and I'm fixing the order to put
render functions in their proper place, so I need to be able to move
these around easily, and making them function calls instead of inlined
makes them easier to manipulate.

desktop_version/src/preloader.h

@@ -3,6 +3,6 @@
 
 void preloaderrender();
 
-void preloaderlogic();
+void preloaderrenderfixed();
 
 #endif /* PRELOADER_H */