By Marianne Rice Like clockwork, as the gray of winter subsides and the showers of April coax the earth to relinquish her green, hundreds of artists around the globe emerge from their studios. Blinking in the daylight, they pack their bags and make the pilgrimage to the annual The Art of the Portrait conference in Atlanta, Georgia. Like the great migration patterns of birds with flawless operation, volunteer staff, distinguished faculty and professional models converged to pu