The referrer spam blacklist has been moved to https://github.com/piwik/referrer-spam-blacklist
This PR integrates the new repository using Composer.
The next step would be to auto-update the list, and let users provide their own list in a
tmp/spammers.txt file for example. Since auto-updating has security implications it might not happen for 2.13.
Looks good to me - this will help the community and us at Piwik to maintain together an up to date Spam Referrers database!