Runs should be reproducable

[sfluegel05]

Tasks

• Make sure the underlying data splits can be reproduced -> see Data handling needs to be restructured #10
• Reproduce specific runs by some seed
  • Lightning should already be using seeds by default, find out where they are stored and how to set seeds manually
  • Check if these seeds lead to reproducible runs (according to @MGlauer's experience, they do not) or if there are other options to guarantee reproducability

[sfluegel05]

I reproduced runs using the same seed and it worked perferctly. I got models with the exact same validation performance. Also, I found out that pytorch lightning changed the default behaviour for seeds.
Before v2.2.0: if no seed is specified, set random seed
After v2.2.0: if no seed is specified, set seed to 0
Thus, one has to set a seed manually with --seed_everything if one does want a different seed.