By Laura McGuire The first female boss of Marks and Spencer, Katie Bickerstaffe, is to step down from the business, the retail favourite has confirmed. Bickerstaffe joined the high-street darling just over two years ago, and has helped lead a massive turn around of the business. She helped run the show alongside chairman Archie Norman and frontman Stuart Machin, who was appointed at the same time as her. An unconventional leadership structure saw Machin named as CEO, and Bickerstaff as co-chief executive. She will depart Marks and Spencer to become a non-executive director at B&Q owner Kingfis…