A basement apartment in Brooklyn. A cat named Jack. A crew of cartoonists who share a studio known as Pizza Island. These are among the people, things and places inhabiting Julia Wertz’s latest graphic memoir, “Impossible People: A Completely Average Recovery Story.” But it is, more generally, a story about the self-deprecating and sometimes curmudgeonly Wertz’s alcoholism and rocky road to recovery as she grapples with depression and an overactive sense of guilt.