Add admin button to file-manager

[rgaudin]

Most users won't know / have access to a user manual, so it would be useful to have either a small parameters icon or anything that symbolizes that or administration on the Filemanager card so that admins can, in fact, know where to start when they want to upload files.

[rgaudin]

This is a report from @Popolechien.

This regards the file-manager when in mixed mode (the edupi mode) where the content is read-only but one can go to /admin/ and be presented with a read-write version to update the files.