Wrote data structure for open nodes list in pathfinder module.
	It is not being used so far.
A* pathfinder now uses new open nodes list data structure for faster lookup
	of cheapest node. Little effect on CPU load, more iterations possible per
	second.
TODO:
	Pathfinding still takes like forever. Examples: 2074 iterations for path length 33,
		1989 for 39, 577 for 20, 1801 for 31, 702 for 19 etc.
Some modifications on inhabitant/pathfinding behaviour.

Path finding could be done in its own threads, maybe. What was it about python
	and multi-threading?