Commit init file

ml-agents/mlagents/trainers/components/reward_signals/__init__.py

 
 from mlagents.tf_utils import tf
 
-from mlagents.trainers.trainer import UnityTrainerException
+from mlagents.trainers.exception import UnityTrainerException
 from mlagents.trainers.tf_policy import TFPolicy
 from mlagents.trainers.models import LearningModel