Fixing the confusion matrices.

This MR fixes an issue in the confusion matrix plotting. The labels in the order [pb, pc, pu] are given. But when getting the truth, for a b-jet the value is 2. But with the current version, if the network predicts a b, the b will be a 0 (due to the index in the order list). This is fixed with reversing the order list only for the confusion matrices. Therefore the correct matching is on.