Function to update individual (existing) comments

[titaniumbones]

I don't currently use the comment API directly when submitting student comments. This is a bit of a mistake and needs to be corrected, but I'm honestly not quite sure how to do it.

API is here: https://canvas.instructure.com/doc/api/submission_comments.html

I will need to track the comment ID in an org property. Maybe not worth doing, I don't know.