DC Comics attempts to expand its universe with the highly anticipated superhero thriller, “Suicide Squad.” While involving, it never quite lives up to its promise. Viola Davis plays a U.S. intelligence big wig who assembles a team of dangerous incarcerated super villains. Her aim is to train them as a military team to use as a last ditch option just in case other super villains invade the Earth. Naturally, the plan backfires and the team members have to clean up Viola’s mess. The terrific, diverse cast includes Will Smith as the assassin Deadshot, Jared Leto as The Joker, Jay Hernandez as firestarter El Diablo, Karen Fukuhara as super samauri Katana and Margot Robbie as wacko Harley Quinn. I, for one, wouldn’t mind seeing Robbie in a stand-alone Harely Quinn movie. Writer/director David Ayer who helmed the action features “End of Watch” and “Fury,” has amped up the violence, so it’s surprising that this exercise in mayhem got away with a PG-13 rating when it obviously deserves an “R.” While it’s just as dark as “Batman V Superman,” Ayer has injected “Suicide Squad” with some shots of welcome humor to lighten the bleak atmosphere. This DC effort hasn’t quite captured the…