Fixes and adjusts various rendering related things.

* Removes linear fog for the time being since it causes various artifacts
* Adjusts blur intensity
* Fixes "lagging bloom" in combination with low FPS
Reduces vignette below water.
Adjusts underwater post processing effect (vignette plus tint).
Adjusts lighting of separately rendered blocks to match the lighting of chunks and sets Bullet Physics maxSubSteps to 8 so blocks won't fall in slow motion in combination with low frame rates.
Tweaks HDR settings and replaces pixel read back operation for the update of the HDR exposure value. Seems to be a tiny bit faster? This is still a clear hot spot performance wise though.
Adjusts water clip plane and disable water reflections for all block sides but the top (this fixes #406).