WIP: Using DGL instead of Torch Geometric

[gennarinoos]

• Update and fix unit tests
• Fix CI environment setup
• Check if point sampler probabilities are negative
• Double check arch changes (graphconv instead of devconv)
• Re-enable surface distance loss
• Re-enable surface distance loss
• Double check algorithm complies with the one on the paper

[martinnormark]

I believe the comment from before does not fit anymore. The function will only return less than k if the number of centroids are less than k. Before we found the k nearest and remove self connections - DGL's function always returns k number of neighbours regardless of exclude self.