We realized that the Kademlia FindNear() function was
1. not using XOR distance (AKA _totally broken_)
2. largely a duplicate of the RoutingTable FindNear() function
Changes in this PR:
1. upgraded RoutingTable FindNear() to use iterator and restrictions
2. removed unneeded RoutingTable interface
3. made Kademlia wrap methods that were previously accessed via RoutingTable
4. fixed the tests