OSLO, Norway — Norway’s prime minister and members of the royal family joined mourners at a memorial service in Oslo Cathedral Sunday for the victims of a shooting in the capital’s nightlife district. A gunman opened fire in central Oslo’s bar area early Saturday, killing two people — a man in his 50s and and another in his 60s — and wounding more than 20 in what the Norwegian security service called an “Islamist terror act” during the capital’s annual LGBTQ Pride festival.