Support for 16bit .png

I believe it would be incredibly helpful if support for saving 16-bit .png files were added. We don’t always need .exr files—many times, working with 16-bit .pngs is much faster for color correction and client delivery. Since the image is already rendered as raw, implementing this feature shouldn’t be too difficult. In fact, I’m quite surprised it hasn’t been added yet, especially considering we raised this request with Chaos multiple times in the past.