Add Chromatic Aberration post-processing stage

[laurelkeys]

Added (lateral) Chromatic Aberration as a new post-processing stage.

This stage has two parameters, for artistic control:

• strength: controls the effect intensity by increasing distortion towards the edges of the image (thus, radially increasing the "color fringes")
• fringing: controls the amount of colors we use for the effect, i.e.:
  • the smallest value will result in the default "three-color split", found in most implementations of CA
  • higher values lead to a more "rainbow-like" effect, as shown in this presentation (see image comparisons below)

Note: "fringing" might be a bad/misleading name.. renaming it to something like "smoothness" would probably be better.

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no aberration	default values

obs.: using a higher strength value than the default for the images below:	lowest fringing	highest fringing