Remove circular dependencies

combo/data/dataset_loaders/simple_data_loader.py

combo/main.py

combo/models/combo_model.py

combo/models/encoder.py

combo/models/utils.py

combo/modules/augmented_lstm.py

combo/modules/encoder.py

combo/modules/feedforward_predictor.py

combo/modules/model.py

combo/modules/module.py

combo/modules/scalar_mix.py

combo/modules/token_embedders/embedding.py

...odules/token_embedders/pretrained_transformer_embedder.py

...n_embedders/pretrained_transformer_mismatched_embedder.py

combo/modules/token_embedders/token_embedder.py

combo/nn/base.py

combo/nn/utils.py

combo/predictors/predictor_model.py