Add feature: output a list of resulting card by order of the most merged/grouped cards

[mbideau]

Currently we can get that information by hacking around the log (if ran in debug mode), with :

❯ grep '^DEBUG \+.* ([0-9]\+ vcards)$' log.txt | sed 's/^DEBUG \+\(.*\) (\([0-9]\+\) vcards)$/\2 \1/g' | sort -nr

It could highlight what card contains a lot of other card merged into it, and that would be a precious info for the user to search for "false positive / wrong merges".