Use per-query ocurrence counts and prioritize them

This way, results are sorted in a way that it is more useful, due to the way
queries are written:

* First, show addresses from the "From" headers of e-mails tagged with
  "addressbook" tag (or whatever tag is configured in the "addrbook_tag"
  field of the Notmuch configuration).
* Second, show addresses appearing in both the "From" and "To" headers.
* Third, show address from the "From" header.

This way addresses from the "address book" and people to whom e-mails have
been sent and received will show first.