By THÉRÈSE MARGOLIS It was a night to remember, and long-remembered it will be. The gala opening of Palacio de Hierro’s stunning new $140 million Coyoacán luxury department store in Mexico City’s freshly remodeled Mítikah shopping mall on Thursday, Sept. 22, not only wowed with its fabulous five-story property, but also with the black-tie reception that no doubt constituted the