ENTERTAINMENT Marguerite Kozenn Chajes has spent nearly a lifetime working on perpetuating the work of Wolfgang Amadeus Mozart VICTORIA BELYEU DIAZ Special to The Jewish News . er name is Mar- guerite Kozenn Chajes, but they call her "Mrs. I...W Mozart." It's not hard to see why. Some 30 years ago, on a Sunday afternoon in Salzburg, Austria, she found herself without a ticket to a sold-out concert she had counted on attending. Having come all the way from America, and because the con- cert was to feature the music of Mozart — one of her favorite com- posers — the talented, Austrian-born singer was especially disappointed. So disappointed, in fact, that she decid- ed she wouldn't be turned away without a fight. Her "fight" consisted of marching herself up to the president of Salzburg's International Foundation Mozarteum, and asking if she might v