Add referral bonus during grading

[renkaichen]

Description

Issues

[crystaltine]

Kinda works, but it only applies the bonus when the last essay is graded, so if someone is referred after their essays have already been graded, the bonus never gets checked, i think.

I think maybe it would be better to just store a separate referral bonus field and do the sum when we rank grading rather than bumping the raw score?

OR maybe we can just have the referral routes also update the application score and then make sure neither route that touches the application score overwrites it (+= instead)