Tweaks some chunk updating and chunk rendering related things in the World Renderer class.

* Removes "maxChunkVBOs" from the config - keeping a minimum of 512 VBOs on the GPU now
* Changes that all chunk VBOs in the area are kept from now on instead of only those, which are in the current view frustum - removes constantly plopping chunks in distant areas while introducing a performance penalty on systems which are not capable of the selected viewing distance
* Fixes that the shadow frustum could never capture the shadows for the whole area since most of the chunks were either not available or not loaded
* Changes that all chunks in the area get queued for updates - and not only those which are in the view frustum... You don't have to keep looking in all directions all the time just to make sure the whole world is actually being loaded