By Simon Mullock David Bernstein was the Manchester City chairman who turned down an offer to merge the club with Wimbledon. His answer was just as unflinching when Scottish giants Rangers wanted to make City their feeder club. It’s fair to say that Bernstein is the man who saved City during their darkest hour in more ways than one – and was also instrumental in the deal that took the club to the City of Manchester Stadium and turned the Blues into a tantalising investment opportunity for Sheikh Mansour. Bernstein celebrated his 80th birthday last May, the day before the team he has supported…