Option to add custom nick replacements [matrix -> irc]

[TomTheDragon]

It would be really useful to have an option to add custom nick replacement rules, so that we could strip/adjust names of bots or users a like.
That would also solve the problem when users use unicode text in their nick, like so "丅工厶乇尺", you could then just add a few rules like this: 丅=T, 工=I, 厶=G, 乇=E, 尺=R