Add some processing-related variables to filename export templates

[seanharding]

Porting over a discussion from discord:

Related to @jboneng PR #721, adding export filename variables for the capture, I'd love to also see more variables about the processing. For example, if I want to export versions with different sharpening settings and keep them straight. Or compare an rgb triplet vs. a narrowband scan (which would of course have different base filenames anyway, but it's not always easy to remember which is which), or different crosstalk matrix settings. But I don't know if we should worry about things getting overwhelming if there are too many template variables...

The suggestion to try to come up with a list of values that makes sense is a good one. I'll give it some thought and come back with some ideas here.