By Dave Itzkoff October 11, 2010 1:50 pm October 11, 2010 1:50 pm How did “The Simpsons” manage to track down Banksy, the pseudonymous British artist, and get him to create the powerful opening-credit sequence from Sunday’s episode, which seems to reveal the torturous sweatshop responsible for the show’s creation? And how, after all that mockery, have the producers behind that Fox animated series