FIREFIGHTERS had to rescue shoppers from a stuck elevator in the super-trendy Prada store in SoHo the other day. A mother and her two young daughters were celebrating one of the girls’ birthdays at the Rem Koolhas-designed boutique at around 4 p.m. when they entered the high-tech, round glass elevator. The thick double doors jammed, trapping them inside for an hour and a half with a mannequin dressed in a see-through plastic raincoat. Since Koolhas neglected to include an escape hatch, the FDNY used a power saw to cut a hole in the steel roof big enough for a ladder. ...