Mayor Bill de Blasio will bundle up and head to Iowa this weekend in his long-shot quest for the White House, The Post has learned. The mayor will arrive in Iowa on Saturday afternoon and depart Sunday afternoon. He expects to have events in Des Moines and Sioux City, though final details are still being worked out, according to a person familiar with the arrangements. The travel comes just a week after de Blasio canceled a scheduled trip to another early presidential primary state, New Hampshire, following the tragic friendly-fire death of New York City police Detective Brian Simonsen. De...