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).
this might run into problems in corner cases. I understand that 'take' takes an Int. I would suggest that if (max - numEnqueuedEver) is > Int.MaxValue then not to use take at all and just return the original nodes.