Dynamically offer every method and attribute of the PyTorch model in the PTModel wrapper

[fcogidi]

The scikit-learn model wrapper (SKModel) currently supports this behaviour using the decorator pattern - if an attribute or method is not found in the wrapper, then the wrapped model is checked.

This should be implemented for the PTModel class as well, so that an instance of the wrapper appears to be like an instance of torch.nn.Module with additional functionalities.