Allow sorting by score in Grade Overview

[berombau]

When reviewing an evaluation, I like to go over the first ones I graded and the lowest graded submissions. This first item I can do by going back to the first submission and unchecking skip completed submissions. The second item I can do by downloading the grade overview and sorting it manually. But a sort button at the grade overview columns in https://dodona.be/en/evaluations/{id}/ would allow me to skip this downloading step.