Add support for recursive variants

[Georacer]

Right now only two levels are supported.

[flyasky]

do you mean sub variants?
like,

variants:
  a:
    common:
       ingredients:
         - [...]
    variants:
      a_1:
        common:
          ingredients:
            - [...]

[Georacer]

I... actually don't remember what I meant 🤣!

Now that I'm getting involved with that other PR I'm sure it will come to me.