SPRINGFIELD — When federal prosecutors unveil a bribery scheme in the state capitol that points a finger at the House speaker, and the speaker has been in charge for 3½ decades, it’s natural that some would turn to a popular but contentious solution: Term limits.The U.S. Attorney’s Office for the Northern District of Illinois unleashed the political thunderbolt this month in announcing that utility giant Commonwealth Edison will pay $200 million to resolve a criminal case which alleges it took part in a decade-long scam …