Remove aggregateNeighbors
Add EdgeDirection.Either and use it to fix CC bug

The bug was due to a misunderstanding of the activeSetOpt parameter to
Graph.mapReduceTriplets. Passing EdgeDirection.Both causes
mapReduceTriplets to run only on edges with *both* vertices in the
active set. This commit adds EdgeDirection.Either, which causes
mapReduceTriplets to run on edges with *either* vertex in the active
set. This is what connected components needed.