Split opennet routing table into short links and long links (refactored)

This is similar to split-opennet-routing-table-original, which is better tested, but cleaned up history and with some minor opennet refactoring included. It does appear to work.
LONG_DISTANCE is chosen as 0.01 because the global link length distribution measured by the probes showed the a good length distribution below 0.01 while showing a flat link length distribution above 0.01. 

LONG_PROPORTION is chosen as 30% for two reasons: (a) It is close to the Kleinberg optimum (around 20%), and (b) it ensures that nodes with 10 connections still have 3 long links, so long links cannot form chains and the routing still scales if the short routing is broken.