Display more informative grade averages when grading by question

[IonMich]

If your feature request related to a problem, please describe.
When grading by question instead of by student, the averages are not displayed until all questions have been graded. This means that will have to grade more than 50% of all the questions before seeing any grade averages, assuming two questions, or even more if the number of questions is greater than two.

Describe the feature you'd like to be implemented
It would be nice to display some temporary statistics, like the current grade percentage, or the individual grade per question averages.