Last week, the Season 3 premiere introduced the slightly new dynamics for Supergirl (Melissa Benoist), especially at work, where her alter ego, Kara Danvers, no longer has Cat Grant as her media-empire boss. (That frees up Calista Flockhart, who plays Cat, to move to better roles, or at least more prestigious shows.) Meanwhile, tonight’s episode of Supergirl introduces a new villain from the DC Comics stable: Psi, who has various mental powers and, in this new TV incarnation, can make peop