Illinois officials have started negotiations with a development group to sell the James R. Thompson Center for $70 million up front, Gov. J.B. Pritzker said Wednesday.Longtime developer Michael Reschke, who leads The Prime Group, will head development of the 17-story building that houses offices for Pritzker and other state leaders. The group plans to retain the design of the 17-story curved glass structure in downtown Chicago.The state plans to keep some office space in the building. Some agencies have already moved to a …