If any of us had a dime for every time someone in the last 13 years has said, "Yeah, but who remembers 'Avatar'?", we'd be rich enough to buy Twitter. For all the times someone has doubted the staying power of the 2009 James Cameron film about a human who learns the ways of an alien culture and eventually becomes that culture's new leader, "Avatar" has stuck around in some form in the cultural consciousness, whether by manifesting doubt that a sequel could ever work especially more than a...