- Added filterVerticesUsingLocalEdges using mask + subgraph way (was about 10% faster on
  livejournal compared to first doing 1) the outer join as done but instead of a Boolean returning Some(vdata) for
  vertices that evaluate to true and None for others; 2) doing a subgraph on the return graph from (1))
- Added a test for filterVerticesUsingLocalEdges
- Added filterVertices and filterEdges as two syntactic sugars over filter (which alread exists) and one test for each.