[MOD] Rules - Disable a class of units at match setup

[BoredRusher]

Hi everyone,

I hadn't played much of 0.28 when I came back, so when hosts typed NCC, NF, NI in the lobby I had no idea what those letters meant and cheerfully kept training those units. Nothing in the game tells you a class is off limits.

So I made a mod that moves the rule to the Match Setup: the host picks Champion Cavalry, Fanatics or Immortals and the class is gone for the whole match. The researches that unlock or improve them go too - but only when every unit they concern is disabled, so `unlock_champion_infantry` always stays.

It is brand new and nobody has played with it yet, so feedback is very welcome. It is compatible with feldmap and autociv.

Install: https://github.com/Atepir/0ad-rules/releases/latest

Limits: only these three classes, a class is global (not per civilization), and units already on the map stay. 

If your group bans something else, tell me which class you would like next.