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.
After some thinking, Separation into current agents and a structure of Occupied may be a relict of the previous design.
I'll try to merge Occupied and Env#env.agents, see if it changes anything with regard to the correctness of the simulation and then try to use a dict for faster operations