text: Title: Cannot save AutoEncoder
  Body: The [official instructions](https://pyod.readthedocs.io/en/latest/model_persistence.html) say to use joblib for pickling PyOD models.
  
  This fails for AutoEncoders, or any other TensorFlow-backed model as far as I can tell. The error is: 
  
  ```
  >>> dump(model, 'model.joblib')
  ...
  TypeError: can't pickle _thread.RLock objects
  ```
  
  Note that it's not sufficient to save the underlying Keras Sequential model, since I need the methods & variables of BaseDetector (like `.decision_scores_` or `.decision_function()`.