It isn’t every day that an attorney writes a full-production musical about Kansas City business history. But that’s precisely the story of Terence O’Malley—owner of The O’Malley Law Firm and the creator and lyricist of the local production “Nelly Don: The Musical.” The performance ran from March 14-31 at the Musical Theatre Heritage in Crown Center and sold out 13 of its 21 shows—making it the most popular box office…