Add a logic viewer

[kbranch]

I'm picturing each node in the logic graph getting mapped to a polygonal area on the map. When a node is in logic, its polygon would be displayed. Nodes could be interacted with to view connections.

Displaying higher logic nodes will take some thought. Color is the easy choice, but somehow working in difficulty shapes would be nice.

Some way to show where specific items are possible to be placed would be neat. Feather couldn't be feather-locked, for example.

This probably needs some upstream changes to give each node a unique ID.