Add "trainable" column

[Enmartz]

Hello, thanks for your useful repository.

I am using a model developed by some users on GitHub and I found that the model has many layers that cannot be trained thanks to this repository. However, I don't know specifically which layers cannot be trained. It would be very helpful if you could add a new "trainable" column to the torchsummary report that shows which of the summarized layers are trainable.

Thanks in advance!