On traits and yields pages combine n, stat and statname columns

See <a href = "https://ebi-forecast.igb.illinois.edu/redmine/issues/2300">Redmine #2300</a>
Unless and until we add a constraint in the database saying that statname can't equal the empty string (or at least can't equal the empty string if stat is non-NULL), we have to test for that case as well.  To see the problem, search the traits page on author Davidson and go to the third result page.  You will see entries like "= 0.4227 , n = 1".