SPRINGFIELD — State Rep. Thaddeus Jones’ name was legally placed on a February primary ballot seeking the Democratic nomination for Calumet City mayor, according to an Illinois Supreme Court opinion released Thursday.But it’s unclear whether the opinion authorizes the Calumet City Democrat to be sworn in as the city’s mayor if he wins the April 6 General Election and remains a state lawmaker, according to an attorney for the city.That’s still in question, because the residents of Calumet City passed a referendum in …