Adds some minor cleanups and rendering tweaks. Also adds a first draft of a z-prepass optimization (currently disabled due to z-fighting issues).

* Changes that all render queues in the world renderer get sorted from front to back or vice versa (currently not needed)
* Renamed transparent chunk pass to refractive pass (since they're treated as opaque chunks and nothing gets actually blended)
* Renamed alpha blend chunk type to refractive
* Renamed renderTransparent() method to renderAlphaBlend() (only entities can utilize real alpha blending at the moment - chunks use the refraction approach)
* Changes that all alpha blend entities are no longer written to the depth buffer
* Cleans up the world renderer debug string to be a bit more compact - and also removes some not too interesting elements