Fix file dependencies in Jupyter Tutorials

[M-Lampert]

With the recent merges #110 and #109, we now provide links to check out our tutorials directly via Google Colab. But there are some errors on Colab due to the file dependencies in some of the notebooks.
Open Tasks:

• Fix FileNotFoundError in temporal_graphs.ipynb
• Come up with a solution to missing files when using Google Colab (temporal_graphs.ipynb, dbgnn.ipynb and paths_higher_order.ipynb)
  Since only the Notebook is opened via Colab, the accompanying files from the repository are not copied over and, thus, an exception is thrown. This could be either fixed by using datasets from Netzschleuder instead or by manually downloading the files from our GitHub Repo in the notebook if they are not available.