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).
for consistency, can this code be same virtually identical to BoolInfoKeeper? (i.e., do not have a separate underlyingMap etc.), hide this type casting in FastUtilUtils (or don't hide it there as well) etc.