Group failed submissions by reason

[robinmaisch]

Feature Description

I suggest grouping the list of failed submissions by reason. For each reason string, I would like the number of corresponding failed submissions and a collapsed list of submission names (preferably one submission name per line; maybe in a scrollable container; maybe with a preview text when collaped such as "Submission753, Submission007, and 85 more" like on the overview view).

Use Case

When examining the failed submissions in the Report Viewer, the different reasons for failure may indicate that the user needs to take action to fix the failure, especially for "could not parse", which may be a syntax error (on the author's part) or an encoding issue (for instructors to fix).
Currently, the list of failed submissions makes it hard to get an overview of the reasons for failures. I would argue that this information is even slightly more relevant than the submission names—at least regarding what users would do about it.

[Kr0nox]

@robinmaisch Would you prefer the sumissions to listed underneath each other or next to each other

Also again with longer names here