Infoflow now will create a complete graph for the policy and then create
a subgraph to filter out nodes based on excluded types and edges based on
minimum weight. The main graph will only need to be rebuilt if there is
a change in the permission map. While this is a little more expensive for
seinfoflow, it should make interactive analysis in apol faster since
repeatedly deriving a subgraph will be faster than repeatedly rebuilding
the entire graph.
