[backend/submissions] Anonymous submissions download

[ogoletti]

In the context of Computing Education Research or for statistics, we are sometimes interested in downloading data about submissions. In most cases, it is necessary to work with anonymized data.

It would be nice to have a button to export/download the submissions without user informations.
Just replacing the user information with an "user"+id whould be enough imho.
That is, it's sometimes important to track which submission has been made by a same user.

[nrybowski]

There is already a manual anonymization tool but it should be directly integrated with the web interface.