New and improved module documentation

Add a lot of missing modules to the API reference and make it a lot more readable, discoverable and tidy.

Before merging into `dev`-branch, please make sure that

[x] the CHANGELOG.rst was updated.
[x] new and adjusted code is formatted using black and isort.
[x] the Dataset-version is updated when existing datasets are adjusted.
[x] the branch was merged into the continuous-integration/run-everything-2022-11-10 branch.
[x] the workflow is running successful in Schleswig-Holstein mode.
[x] the workflow is running successful in Everything mode.