Blender Git Loki

SSAO introduce quality settings

Basically change the way SSAO samples the screen by using a circular
filter instead. This is inspired by HBAO though we still don't use this.

The quality settings change the number and density of samples. We can
definitely improve things here though.

We also jitter the sampling locations per pixel. Generally this adds a
kind of noise. Some banding is, unfortunately still apparent and small
distances will introduce noise. This can be fixed but I will have to see
if it can be done without much of a cost.