Merge vocexcel-parts used by voc4cat-tool

[dalito]

Abandoned in favor of #119

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/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 templates/VocExcel-template_043.xlsx \
  --path-rename templates/VocExcel-template_043.xlsx:tests/templates/VocExcel-template_043.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).