Rebecca Rubin Film and Media Reporter Lionsgate is officially inviting audiences back to Panem for “The Ballad of Songbirds and Snakes,” a prequel set in the “Hunger Games” universe. At long last, the odds were ever in CinemaCon-goers favor on Thursday as attendees of the annual trade show for theater owners were treated to the first teaser for the spinoff story. At last year’s convention, the studio only brought a short clip (sans movie footage or even a cast list) of “The Ballad of Songbirds and Snakes,” which left much to be desired. The trailer begins with Viola Davis, who plays the head gamemaker Volumnia Gaul, introducing “the creators of the Hunger Games themselves.” But there’s a change in this year’s dystopian event, warns Academy dean Casca Highbottom.