Modernize nav packaging

[hmpf]

First steps in modernizing how nav is built and packaged.

[codecov]

Codecov Report

Merging #2655 (3d9e2fe) into master (83224bf) will increase coverage by 0.50%.
Report is 56 commits behind head on master.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2655      +/-   ##
==========================================
+ Coverage   54.61%   55.12%   +0.50%     
==========================================
  Files         560      561       +1     
  Lines       40712    41459     +747     
==========================================
+ Hits        22235    22854     +619     
- Misses      18477    18605     +128     

see 13 files with indirect coverage changes

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[lunkwill42]

We should definitely look into improving how the SASS build process works.

[hmpf]

This PR picks the low-hanging fruit. It does not:

• Move script installation from setuptools/setup.py to pyproject.toml #2676
• Modernize how css-files are generated from sass-files
• Update author/maintainer to golden addresses/names
• Set up a workflow to build pypi packages
• Update docs

[lunkwill42]

This works just fine with test suite and inside the dev containers. I will try to test Debianizing it.

And, I assume perhaps the install guides need to be updated just a tiny bit (the "install from source"-ones)

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

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