Easier configuration for models and support for getting hidden layer outputs

Added

• Added option to get hidden layer outputs and embedding outputs with ClassificationModel.predict() method.
  • Setting config: {"output_hidden_states": True} will automatically return all embedding outputs and hidden layer outputs.

Changed

• global_args now has a config dictionary which can be used to override default values in the confg class.
  • This can be used with ClassificationModel, MultiLabelClassificationModel, NERModel, QuestionAnsweringModel, and LanguageModelingModel