PARIS — Smoke and reflective glass never really go out of fashion and when designer Alexander Wang had built his Balenciaga runway for Spring 2015 he specified as much. In the end the glass was see-through, which meant the smoke underneath was visible to create an effect that the models were quite literally walking on air. Delicate embroidery for this collection demanded nothing less. On the night of Wednesday underneath a tent at 18 Avenue de New York before tightly selected audience (there wer