Country Standard Time: Iris DeMent in concert DeMent finds vision in voice and song Side Door Club, St. Louis, April 16 By Roy Kasten St. LOUIS – When Iris DeMent walked on stage at the sold-out Side Door, sporting a burgundy dress and an abalone-glinting Martin, she smiled, plugged in and without further word strummed “Let the Mystery Be,” a statement of personal philosophy and the perfect introduction to her music. “Boy, you’re all sure a surprise,” she said when…