SPRINGFIELD — The Illinois House on Wednesday elected its first Black speaker to replace the longest-serving legislative leader in modern U.S. history, picking Democratic Rep. Emanuel “Chris” Welch for the job and pushing aside Michael J. Madigan after he was implicated in an ongoing bribery investigation.Welch, an eight-year House veteran from Hillside, garnered 70 votes from the 118-member House just days after emerging as the front-runner alternative to Madigan, 78, who was first inaugurated as a House …