Family tree visualizer/editor

With structured relations between characters, we should also have a way to visualize families in a family tree view. The easiest way to implement this would be a read-only view, but it'd be great if there were some way to actually edit those relationships as well. I have no idea what the UI would look like though. Thoughts?

The issue names no files, tests, or entry points. Start by reviewing the existing character relationship and family views, then clarify whether the first milestone is a read-only family tree or relationship editing; completion depends on agreeing on the UI and scope.

Written by the indexing model from the issue text.