Suppress reviewer IP addresses and tokens from solr logs

Checks if the http referer contains `token=...`, and if so, suppresses the IP/DNS address from the solr statistics log. Also replaces review tokens with a dummy value (all zeroes)

Includes test cases for token detection and replacement.

See [Trello 238](https://trello.com/c/kBHeNHs4/238-urgent-reviewer-ip-addresses)

Also adds functionality to StatisticsClient (`bin/dspace stats-util`) to clean the identifiers out of an existing solr index