Copenhagen’s “8 House,” an ultramodern loop of apartments created by architect Bjarke Ingels, reinvents the concept of “home.” Its 500 residents can traverse all nine floors by bike while their kids attend kindergarten on the ground floor. This exuberant documentary profiles the (mostly) happy residents, including a group of children who experience the best scavenger hunt ever, offering a hopeful, inspired picture of communal living by design.