By Tim Gaynor WACO, Texas (Reuters) - President Barack Obama will assume a familiar role consoling family and friends of disaster victims on Thursday when he speaks at a Texas memorial for firefighters killed in a massive explosion at a fertilizer plant. Just a week after he traveled to Boston following the Marathon bombing that killed three people, he will speak at a memorial on the campus of Baylor University in Waco to honor the 11 first responders who died in the blast. ...