To Worcester residents, the retail stores of their childhood are the stuff of nostalgia; most among them have a memory of that special birthday gift, back-to-school shopping or a special outfit jaunt at one of the many Worcester stores that are now a memory, like The Mart: Denholm & McKay, Filene's, Jordan Marsh; Grant's, Woolworth's or Spags in Shrewsbury (a trip most of us made at one time or an