Merge vocexcel-parts used by voc4cat-tool (v2)

[dalito]

This is an improved version of #117.

This PR contains an experiment to merge the parts of VocExcel that we use. This has several advantages compared to further maintaining our fork of VocExcel. Future changes will affect just one code base which makes development a lot easier. Also it helps to avoid confusion with different VocExcel (ours and RDFLib/VocExcel). Moreover, we no longer use the term Excel™ as part of a "product" which IMHO is problematic.

I have merged the respective files including the full git-history to this PR´s branch. Some files/directories were moved to match the directory layout of this repository. The following command was used to rewrite the history in a local clone of NFDICat/VocExcel:

git filter-repo \
  --path tests/043_exhaustive_example.xlsx \
  --path tests/043_exhaustive_example_perfect_output.ttl \
  --path tests/043_simple_valid.xlsx \
  --path tests/test_models.py \
  --path tests/test_template043.py \
  --path tests/test_utils.py \
  --path .pre-commit-config.yaml \
  --path vocexcel/convert.py \
  --path vocexcel/convert_043.py \
  --path vocexcel/models.py \
  --path vocexcel/profiles.py \
  --path vocexcel/utils.py \
  --path vocexcel/validator.vocpub.ttl \
  --path vocexcel/blank_043.xlsx \
  --path-rename tests/043_exhaustive_example.xlsx:tests/templ_versions/043_exhaustive_example.xlsx \
  --path-rename tests/043_exhaustive_example_perfect_output.ttl:tests/templ_versions/043_exhaustive_example_perfect_output.ttl \
  --path-rename tests/043_simple_valid.xlsx:tests/templ_versions/043_simple_valid.xlsx \
  --path-rename vocexcel/:src/voc4cat/

The tool git filter-repo can be simply pipx-installed: pipx install git filter-repo (at least on Windows).

I will mark this as a draft. Still to do:

• Change imports etc. to use the merged VocExcel code.
• Clean up merged VocExcel-code that uses code that was not taken over.
• Switching from MIT to BSD-3-Clause license since VocExcel uses BSD-3-clause-license and having to licenses is confusing.

After merging:

• Archive NFDICat/VocExcel