Move examples to tutorials

[janfb]

• move the two examples into the tutorials/ folder, adapt all links
• go through all tutorials and reorder them with increasing numbers, group them by topic (a bit), fix all links
• add implemented methods to landing page.

Problem: we sometimes link between tutorials, but it is not clear whether we should use the notebook links, or the markdown links of the converted notebooks. I now decided to use the markdown links, i.e., on the website the links smoothly refer to the corresponding tutorial on the website. However, when clicked in the notebook, e.g., when running the notebooks locally, the link will not work (because it links locally between the docs markdown files. As a help, I changed the link text to contain the tutorial number and name explicitly, so that it will be clear which tutorial we are linking to.

[michaeldeistler]

when running the notebooks locally, the link will not work I think that's fine

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.87%. Comparing base (b3254ed) to head (6fc91ca).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1231      +/-   ##
==========================================
- Coverage   85.44%   76.87%   -8.57%     
==========================================
  Files         101      101              
  Lines        7941     7945       +4     
==========================================
- Hits         6785     6108     -677     
- Misses       1156     1837     +681     

Flag	Coverage Δ
unittests	76.87% <ø> (-8.57%)	⬇️

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