Improve censor rules created by anonymise and close user account operation

[RichardTaylor]

Following the closure of #3074 this is a new ticket for improving the censor rule created on the automated anonomising and closing of an account.

The issue is a censor rule for "Fred Blogs" doesn't catch mentions of eg. "Mr Blogs" in the text.

Consider cases where a name (surname or firstname) is a common word; and that some user-names can contain initials, some usernames are names of organisations etc.

Logic eg. having a separate censor rule for each "word" within a username of 4 or more letters might suffice in the vast majority of cases; and administrators can always delete/edit automatically created censor rules and create replacements.