Merge branch 'setsumbt' into 'master'

.gitignore

convlab/dst/evaluate_unified_datasets.py

convlab/dst/setsumbt/dataset/unified_format.py

convlab/dst/setsumbt/distillation_setup.py

convlab/dst/setsumbt/do/nbt.py

convlab/dst/setsumbt/loss/endd_loss.py

convlab/dst/setsumbt/modeling/ensemble_nbt.py

convlab/dst/setsumbt/modeling/training.py

convlab/dst/setsumbt/predict_user_actions.py

convlab/dst/setsumbt/tracker.py

convlab/policy/mle/loader.py

convlab/policy/mle/train.py

convlab/policy/ppo/setsumbt_config.json

convlab/policy/ppo/train.py

convlab/util/custom_util.py