Compute PESQ in background; add tqdm progress bar

[jonashaag]

Hi! Thanks for this nice implementation, I've used it as a basis for my own experiments.

I added two features:

• Computing PESQ in background to speed up training
• Tqdm progress bar for nice training progress. This gives you a progress bar like this while also retaining the original logging logic.

  Epoch 7 train batch: 100%|███████████████████| 5000/5000 [1:17:52<00:00,  1.07it/s, loss=-2.42, pesq=2.86]
  Epoch 7 val batch:  42%|████████▉               | 627/1500 [04:30<06:23,  2.27it/s, loss=-4.95, pesq=2.63]

I know it looks like a lot of code has changed but that's mainly due to indentation. If you like the changes feel free to merge :)

[jonashaag]

Note you can also hide whitespace changes in GH by adding ?w=1/&w=1 to the diff URL