Allow submiting ignored code through info.csv

[rien]

Since #1524 we allow ignoring boilerplate / template code by submitting an ignore file. Fingerprints matching with this file will not count towards plagiarism. This is feature can currently only be activated through the CLI.

By adding a field ignored to the info.csv, we could also activate this functionality in other places where Dolos is used (e.g. the Dolos server).

This requires changing the Dolos#fromCSV function to handle an ignored field. The function should be changed to also return this ignored file in addition to the parsed files.

Since we currently only support single-file submissions, it makes sense to throw an error if multiple ignored files are added, as this is possibly a user error. If we want to make this less strict, this could also be an error, but this is less visible.

[mikaelGusse]

Added in this PR