include copies of URL visit and nohead lists in scan results

[a11ya11y]

The results folder generated from each scan contains a mostly complete collection of everything needed to reproduce the scan. While the URLs visited can be retrieved from the pages_scanned.csv, it would be nice to reproduce the CSVs from the /base_urls/visit and /base_urls/nohead directories.

In the case a scan uses multiple visit and/or nohead CSVs, I think it'd be sufficient to concatenate these into single CSVs.

In terms of filenames, what about base_urls_visit.csv and base_urls_nohead.csv? Or, given #145, audit_subject_visit.csv and audit_subject_nohead.csv?