extend visualization of filtered subgraph

[mjsduncan]

after filtering via double-clicking a node to show just that node and it's containing links, it would be cool to hover over another node (say whiling holding ctrl) to show that node's containing links. then double-clicking that node would extend the visualized sub-graph to include the revealed links and nodes. in the attached messy example, hovering over the node pointed to by the green arrow would reveal the red nodes and links and allow them to be added to the visualized sub-graph.