Doc: Clean up visualization examples

[dweindl]

The visualization examples were pretty redundant. Merged them into a single notebook. Removed redundant blocks.

Furthermore:

• Don't use deprecated Problem.from_files
• Simplify by not loading all files separately
• Fix grammar / typos
• Add replicate plot example
• Make plots more readable
• ...

:eyes: https://petab--236.org.readthedocs.build/projects/libpetab-python/en/236/example/example_visualization.html#

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (1bebd15) 76.30% compared to head (e292d2d) 76.30%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #236 +/- ## ======================================== Coverage 76.30% 76.30% ======================================== Files 34 34 Lines 3191 3191 Branches 774 774 ======================================== Hits 2435 2435 Misses 554 554 Partials 202 202 ```

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