Primitive chromatic aberration effect for env_screeneffect

[Blixibon]

This PR adds two new effect types: Chromatic Blur and Chromatic Aberration. The former overlays 3 different frames of red, green, and blue tints respectively with different offsets. The latter does the same thing, but stretches the frames to distort colors based on how far away they are from the middle of the screen. Parameters like the offset or tint of each frame can be modified via cvars prefixed by r_chromatic_aberration. The effects themselves are controlled by env_screeneffect, and they start at 100 to avoid conflicts with any potential mod effects.

Note that I am not experienced with post-processing elements and there are likely better ways of programming these effects. I originally developed these for an Entropy : Zero-related project, but I decided to try bringing them to Mapbase because a generic chromatic aberration effect could come in handy for other designers.

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No effect active:

Chromatic Blur:

Chromatic Aberration:

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PR Checklist

• My PR follows all guidelines in the CONTRIBUTING.md file
• My PR targets a develop branch OR targets another branch with a specific goal in mind

[1upD]

LGTM, love this