Allow searching to return complements if needed

[fedarko]

For when #67 is implemented. If the currently shown component contains node -N but not node N, and the user searches for node N, then show -N. This should also work with the vice-versa case.

... This would probably be more intuitive if we named nodes the same way Bandage does (N+ and N-), making this relationship explicit. But I guess that's an issue for another day.