Edge Weight Representation

[M-Lampert]

In the previous versions, we saved the number of times each walk or DAG appeared as a count/weight. This would translate to a graph feature for each PyG Data object. For the path statistics, it is probably more convenient to have the count/weight as edge weight. At first we added it in both ways for all representations were it is possible, but that leads to an error when using the PyG DataLoader in MultiOrderModel.from_DAGs. This is fixed for now (#154) but we should think about what representation is best also thinking about the order detection (#107).