Replace pythonjob task by normal task, drop usage of pickle_node (#35)

* Use pyfunction

* use int for node name in the edges

* Run the relevant notebooks

* Bump aiida-workgraph to 0.5.1

* Install AiiDA WG from pip in environment.yml

* fix environment.yml

* Also change aiida_simple workflow to use new setup.

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Co-authored-by: Julian Geiger <julian.geiger@psi.ch>

Author: superstar54