Added torch model and training pipeline

[LucaMalagutti]

This pull request adds a Pytorch version of the TIMNET architecture together with extendable training and evaluation pipelines that follow the already existing code relying on TF/Keras.

This addition could be useful to users that are more familiar with the torch ecosystem.

[hwang9u]

Nice work!!!

[whh07141]

Hello author, I reproduced your code, but the test results are very poor and the loss on the verification set does not decrease. Could you please tell me about your parameter settings?