The former head of the Maine Turnpike pleaded guilty to theft charges Thursday afternoon in a Portland courtroom. Paul Violette appeared in court around 3 p.m. He is charged with unauthorized use of turnpike gift cards and using turnpike authority credit cards for personal travel, meals and other expenses. Violette’s attorney said his client agreed to plead guilty in exchange for a prison sentence not to exceed five years. Violette resigned last March after 23 years as executive director amid allegations of lavish spending and misappropriation of turnpike funds.