CHICAGO — Jesse Jackson Sr. visited the Cook County Jail Saturday morning to speak to a gymnasium filled with inmates. Despite a voice growing quieter in an eight-year battle with Parkinson’s disease, the civil rights leader’s message of hope rang clear. “I want you all to plan to get out,” Jackson said. The 81-year-old shook the hands of dozens of the 241 incarcerated men and women in attendance as he was pushed in a wheelchair around the drab white room that became suddenly filled by a band’s joyful gospel music. Visiting the jail after rescheduling his annual Christmas Day trip, the Rainbow…