Blank nodes returned during expansion are not being recognized

Getting the neighbor counts fails when one of the neighbors is a blank node.

## Reproduction steps

1. Connect to nobelprize.org connection
2. Add first Nobel laureate to the graph `nprl:618`
3. Expand the node

Fetching the neighbor counts fails

## Investigation

The results of the neighbor expansion includes on blank node as the `?object`. This eventually is turned in to a `Vertex` that is not recognized as a blank node. Then the neighbor count query will include the blank node pseudo ID in the list of resources to fetch, which fails.

After digging a little deeper, I believe the fix is to add more data to the `ResultEdge` about the source and target vertices. This will aid later in the pipeline when those vertices are expanded to full vertices. However, this will need some special handling since the vertices are blank nodes and can not be queried directly.