NEW GLAMOUR Spring's recipe for OPULENT ELEGANCE calls for a dash of flash and a bit of 1970s swagger, topped off with fun gold flourishes Photographs by TO/Vi MUNRO Embellished tulle is sheer genius. THiS PAGC: Top. $4,7?5. Givenchy by Riccardo Tisci. Barneys New York; 888-8-BARNEYS. Br