make nomenclature for color mix consistent

[earthbound19]

For scripts related to color mixing in some amount between two colors, scripts variously are named or use the terms:

• augment
• interpolate
• gradient
• blend
• ?

Change all of these, with consequent renames in called scripts from code in other scripts, to one of them. Maybe "interpolate," or the much more accessible and maybe memorable "mix".

Extend this to adjacent terms like "shade" as in getNshadesOfColorCIECAM02.py?