Gaussian blur post processing material

@plangton by extending the kernel fruther, but it already is huge. The current 15x15 matrix gives you 225 sampling points per pixel, that will be taken for every pixel on your 1920x1080 screen. Ugh?! I suggest you to try to find an approximation to this method that takes significantly less samples there you can have the freedom to extend it even larger, thus making it stronger.