New features (still valid if we integrate with ASB) - splitting the block list

[Zodiac1978]

There some limitations/known issues in the underlying blacklist:
https://github.com/splorp/wordpress-comment-blacklist#known-issues-limitations--other-gotchas

Maybe we can solve them if we provide more options like:

• add URL shorteners
• add WordPress stuff links
• add non-english keywords

Although I don't know how to extract these strings which are all in the big blacklist.txt file.

And we shouldn't overwrite manual added strings:
https://wordpress.org/support/topic/manual-blacklist-overwritten

Maybe we can just append them to the manual added ones.