Standardize Y and Z coords

[dbierek]

Right now, in some places Y is vertical and Z is horizontal, and in other places Z is vertical and Y is horizontal.
Recast uses Y as vertical and also sets the Z coord to be negative relative to Hitman's Y coord.
In all places throughout NavKit, the Recast coordinate system should be hidden away, and Hitman's coordinate system should be used:
X and Y are horizontal, and Z is vertical.