minor fixes for geometry compuation during boundary ranking

minor fixes for geometry compuation during boundary ranking

Go back to using centroid when determining if one admin level
is within another. There are cases where boundaries are slightly
misaligned due to mapping errors (not using the same ways in the
relations).

Only declare boundaries the same when they have the same wikidata
tag _and_ have exactly the same geometry. This works around tagging
errors with the wikidata tag, which happen because of automated
edits to the wikidata tag.