Celtic managers past and present will be remembered for their colourful spells at Parkhead, some gaining more adulation than others. Martin O’Neill would come in right at the top of that bracket, and his influence during a five-year reign in Glasgow’s east end helped set the scene for Celtic’s dominance of Scottish football in the 21st century. The 72-year-old claimed three Scottish Premiership titles, three Scottish Cups and a Scottish League Cup at the club, restoring a conveyor belt of silverware missing for much of the previous decade. Of course, he also led Celtic to the UEFA Cup final in…