Celtic need to focus their summer rebuild around the talent of David Turnbull if they are to bounce back from a disastrous season.A £3m summer signing from Motherwell, the 21-year-old has been one of the few bright spots for the Hoops amid a season of turmoil that has seen them drop 18 points behind leaders Rangers.The midfielder has notched seven goals and six assists in 26 appearances in his debut season in Glasgow and now looks an essential part of the club's long-term plans.Former Rangers