Add/remove individual values instead of changing the whole list setting

[sbxte]

Closes #418

[MineGame159]

I don't like how you made the "toggle" behaviour be the default. It goes against how every other setting works and IMO this should be done with sub commands like the issue says.

Also I am not a big fan of not creating a new ArrayList in the parse methods because they should not modify the current state of the setting as the caller is responsible for actually setting the value or rejecting the new value. But I guess it is fine because that can never happen with those settings.

[sbxte]

Hmm. Guess I'll rewrite it with command argument builder instead.