feature/outer kore

**please review**

outer KORE sketch. will probably change as we start using it.
It is leftover from when we had configurations. I will remove it.

(short parenthesis: eventually, we'll need some sort of special data structure representing the configuration -- all clients need it, and having a special class makes common operations easier. As long as it implements the right interfaces, it will still retain all the benefits listed under 
https://github.com/kframework/k/wiki/KAST-and-KORE#cells-configurations-and-configuration-abstraction
I.e., configuration terms could still be treated like regular terms.)

In any case, I will remove it, and we can have this discussion when we'll be pressed by it.