(Reuters) -Boeing CEO Dave Calhoun will step down by year-end in a broad management shakeup brought on by the planemaker's sprawling safety crisis exacerbated by a January mid-air panel blowout on a 737 MAX plane. In addition, board chair Larry Kellner and Stan Deal, head of the company's commercial planes business, are also leaving as Boeing's board tries to get control of the myriad issues that have shaken confidence in the iconic planemaker over several weeks. Immediately after the Jan. 5 pan