Improved traversers

Added abstract class QueueBasedTraverser holds general logic for most
traversers.
Fixed errors in InfoKeepers.
Added InfoKeeper that uses IntToBoolean fastutil map to store Boolean
values.
Changed BreadthFirstTraverser so that first node is the node we start
traverse from (to be consistent with other traversals).
that is not so simple. Think of a situation as above. I was thinking of some ways to limit the queue size, but haven't found any clear and computationally cheap solution.