Use 'blocklist' instead of 'blacklist'

The word 'blacklist' comes from the medieval term 'black book'. However, since 'black' is now used to describe people we should avoid additional negative associations with it. Use 'blocklist'.

See also: https://www.zdnet.com/article/github-to-replace-master-with-alternative-term-to-avoid-slavery-references/

See: tracker-miners#112 (closed)