A police officer who was left in critical condition after a mass stabbing in the German city of Mannheim on Friday has died, local authorities say.The 29-year-old was one of six people, including anti-Islam activist Michael Stürzenberger, to be wounded by the attacker, who was detained at the scene. The police officer was stabbed several times in the head. Despite undergoing emergency surgery, he succumbed to his wounds on Sunday afternoon.”This news has shaken me to the core,” said the leader of Baden-Württemberg, the state in which Mannheim is located.”All our thoughts are with the…