Summary of activity in grading view

As part of an early step towards better reporting for instructors on student activity, a potential quick win would be providing instructors a summary of activity (# annotations, # replies) in the grading view.

Here's what this looks like in [Harmonize](https://help.harmonizelearning.com/hc/en-us/articles/16785013000717-Graded-PDF-Annotations):


This could potentially be connected to "participation grading": allowing instructors to pick a number of annotations and then count the student annotations for them against that number and automatically report the assignment as complete or full credit.