Add option to output Geometrical PSF to an EXR file

[devshgraphicsprogramming]

There's a dearth of high dynamic range, unclipped, centered, long falloff, high resolution lens flares to use with UE4-style FFT convolution bloom.

I think LensSim could be a great tool to synthetically generate such convolution kernels (I know, not exactly physically accurate as the PSF varies depending on position on the lens + chromatic aberration is not symmetrical)