Notebook 01 mse2023 feeback

[agoscinski]

lab-cosmo/chemiscope#269 (comment) in this PR

• adapt error message of ex 3 saying wrong unit cell
• improving in-notebook formatting for pbc-1.png and pbc-2.png

Open bugs

• error messages in widget code input are not correctly shown to student, I think this is because widget code input fixed this in version 3.5.0, but we are using 3.0.0 because it the new version caused bugs, and in scicode-wigdets we removed it already. So I think we should temporary put it back here. Would fix this in a different PR
• unit cell is not shown in chemiscope for some people on noto, chemiscope version is the same (0.5.1) and ase (3.22.1), pbc is True, cell is the same, discussed in Missing unit cell option in chemiscope jupyterwidget viewer lab-cosmo/chemiscope#269 (comment)