Defaults for Density Shading

[BradyAJohnston]

Discussed a bit in #383, we should also include a number of color maps or LUTs for shading density. It would be best for these to match already existing standards in coloring, but also some more artistic versions.

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An example that implements a similar kind of thing by providing a number of color ramps for matplotlib palettes: https://github.com/TheJeran/Blender-Colormaps