Fabian Balsiger

We need to verify if the references and predictions for categorical metrics are of type integer or boolean. This affects all metrics in the `categorical` module and the `SegmentationEvaluator`.

Add balanced average Hausdorff distance metric (bAHD)

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A recent publication introduced the balanced average Hausdorff distance (bAHD) metric, see [https://arxiv.org/abs/2009.00215](https://arxiv.org/abs/2009.00215). The metric was also added to the [EvaluateSegmentation](https://github.com/Visceral-Project/EvaluateSegmentation/commit/1e65f0c43796a0f5e63634f4a39aa769c47c3c95) repository. Consider adding once the publication is accepted.

Currently, the `AverageDistance` metric is implemented using SimpleITK. As it is the last metric relying on SimpleITK, removing the SimpleITK dependency from the metrics would be quite neat. - [...