In EvalFunction, defining elevationAtGridLocation(), and using it in
overallHeightMetric() and in heightFluctuationMetric(). Meanwhile I found a
blaring problem in overallHeightMetric(), which had to do with the computation
for maxAltitudesPossible, which used the z-dimension twice instead of using
the y-dimension. This has been fixed, and the linear factor
OVERALL_HEIGHT_METRIC has been changed to compensate for the correction.
