more clever splitting of closed ways

if a way is closed, iD needs to choose a second node to
split the way at.

This algorithm looks for a node that is both far away from
the initial node in terms of way segment length and nearby
in terms of beeline-distance. This assures that areas get
split on the most "natural" points (independent of the number
of nodes).

For example: bone-shaped areas get split across their waist-
line, circles across the diameter.
Add iD.geo.sphericalDistance

iD.geo.euclideanDistance should only be used for calculations of 
projected coordinates or display (pixel) coordinates.

iD.geo.sphericalDistance calculates approximate geographical 
distances, accounting for distortions at higher latitudes. This 
can be used for determining the nearest node (operations.Delete,
actions.Circularize) or relative length comparisons (actions.Split).
Clean up