Boeing CEO David Calhoun will step down from the embattled plane maker at the end of the year as part of a broad management shakeup Monday after a series of mishaps at one of America’s iconic manufacturers.Stan Deal, president and CEO of Boeing’s commercial airplanes unit, will retire immediately. Stephanie Pope, the company’s chief operating officer for less than three months, has taken over leadership of the key division.The company said board Chairman Lawrence Kellner, a former airline chief, won’t stand for re-election …