ISP editing pipeline

[DanielNobbe]

After adding noise, we should do the standard camera modifications.

• Demosaicing (convert RAW to RGB) #13
• White balance
• Exposure
• Naive denoising?
• Others, see https://github.com/timothybrooks/unprocessing/blob/master/process.py

Note that if we target pro photographers, we might want to only do demosaicing, or even operate directly on RAW files.