DETROIT — Oxford Community Schools had staff members trained on threat assessment practices outside the district, but never established teams or used any of the tools designed to avoid school violence before the Nov. 30 attack, two former board members alleged Monday. Oxford board President Tom Donnelly and former Treasurer Korey Bailey made the accusation Monday, saying they both began to research school safety measures in the months after the shooting and learned the district didn’t follow policies it had in place that could have prevented the attack that killed four students at Oxford High …