ENH: Add cerebparc segmentation script fixed DiceCE/Hausdorff weights

[jhlegarreta]

Add cerebparc segmentation script fixed DiceCE/Hausdorff weights.

[jhlegarreta]

The Hausdorff (distance map-based) loss computation requires large amounts of GPU memory, and the scripts fail frequently at

File "/home/jhlegarreta/src/dmriseg/scripts/train_cerebparc_scheduler.py", line 436, in <listcomp>
    w * loss_fn(outputs, labels)
        ^^^^^^^^^^^^^^^^^^^^^^^^

even when using the 24 GB GPU.

That is why many of the Hausdorff loss computation implementations that I have seen accept an idc or index parameter, so that the distance map-based losses can be computed separately for each label, and then be added. Something to be taken into account.

Applies to PRs #37, #38 and #40 as well.