feat: add to GF Pregel an optional ability to stop earlier based on vertices voting #573

It is important at least for the following algorithms:

• LabelPropagation (feat: LabelPropagation without GraphX #564): if for all the vertices, label did not change at the iteration we should stop
• PageRank (feat: PageRank without GraphX #569): if for all the vertices, change in rank less than tolerance at the iteration we should stop