Add a config that's more lenient for OOP

[nickserv]

I understand the recommended config's decision to ban classes, but this plugin exposes a lot of useful options to allow OOP style while preventing too much mutation outside of object construction. I think it would be useful to expose a plugin:fp/oop config with classes, this mutation, and similar options enabled.

If you agree I can make a pull request (and just to be clear, this would not be the default config).