AiCombat pathfinding enhancement + z-moving in water/air combat

1) Enemies now will try to use shortcuts as often as they can so they won't fall into the river in Balmora for example, also they won't move in robotic fashion from one waypoint to another but run directly on target (if there are no obstacles/pits). System works while target is in line of sight (else use pathgrid).
2) you can completely disregard commit "enable z-moving for flying/water combatants" but rather look at "remake of z-moving in combat for flying/swimming enemies" to understand z-moving (done through x-rotating)
Note: There are some minor fixes in large 'merge' commit:
https://github.com/mrcheko/openmw/commit/6a3dddfb9aa47579b73357bc43537c7497867e59#diff-2726f39499988de80684e08ca85615bdR15; https://github.com/mrcheko/openmw/commit/6a3dddfb9aa47579b73357bc43537c7497867e59#diff-cd5864019599ad43105834ee07ed1699L42