Include URI scheme in output CSV

It might be interesting to calculate statistics on the use of HTTP
vs HTTPS, for example.
Redact complete URIs from the output unless they’re local

To preserve kids’ privacy, only include the full URIs from the
browser history for local files (which are likely to be part of
collections, and hence it’s useful to see how the collections are
being used). For non-local URIs, only include the domain name and
scheme.
Hash the XO serial number before output to the CSV

This slightly improves anonymisation of the outputted data, without
affecting its statistical usefulness significantly. Anonymisation
is nowhere near perfect, however, and given a bit of work it would
be possible to trace activity instances back to the kids.