Slip Days Tracker Improvements

[cycomachead]

Instead of checking for certain params, create a function hasGoodGuess
or something, that can check the assignment / submission details if we can
generate a good guess for whether the submission time can be trusted.

Things that aren't trustworthy and should return unknown:

• student commented with an attachment
• assignment has_overrides is true

anything else?

[aaaschmitt]

I've actually updated the slip day tracker to look for overrides.

The only thing we may be missing is if they submit via a comment (attachment in comment section).