Reordered methods in WorldRendererLwjgl class. No functional changes.

* General reordering to reflect the renderer's lifecycle (pregenerate, update, render, dispose)
* Related methods are now near each other, with callers usually listed first and called methods listed immediately afterwards.
* Accessors (getSomething, setSomething, isSomething) are now close together at the end of the class. 
* No changes to the methods themselves nor to the variable declarations and constructor at the beginning of the class.

This commit paves the way to split the class into two separate interfaces/implementations, one for rendering, the other for keeping renderable chunk meshes up to date. I could have split the class right away but the diff would have been pretty messy and hard to read. A preliminary reordering will make future diffs easier on the eye.