Tweaks various rendering related things and improves light shaft and SSAO artifacts.

* Increases default light shaft sample count from 64 to 128
* Increases default SSAO sample count from 16 to 64 (SSAO is only available on the highest video setting from now on) - we could provide a video setting for the sample counts later on
* Improves SSAO depth related artifacts by offsetting the generated SSAO hemisphere samples further from the center