Clara and Mr. TiffanyBy: Susan Vreeland NATIONAL BESTSELLER Its 1893, and at the Chicago Worlds Fair, Louis Comfort Tiffany makes his debut with a luminous exhibition of innovative stained glass windows that he hopes will earn him a place on the international artistic stage. But behind the scenes in his New York studio is the freethinking Clara Driscoll, head of his womens division, who conceives of and designs nearly all of the iconic leaded glass lamps for which Tiffany