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.
It's not needed unless you are passing here some ants, that should not be moved or were already moved (just as in the partitioned model `parallant_tiled.erl`).