Simplify/refactor operators

The partitioning code and tiled model are refactored along to the description in the ParaPhrase deliverable D6.8 (chapter 4).
I fixed a bug which sometimes caused losing agents. Now there is an issue with deadlocking (#1) but it's not a bug.

The tile version divides the world into 2 pieces, and it requires the width to be even.
Set would not be best for this, since Ant have additional state (direction), and not just position.  It would allow multiple Ants at same point, just until they look different ways.

I guess we will try to go with Dictionary, where position would be a Key, and we could not really care about Value; just pass it around ant let it be defined by user/model.