Fix issue with tfoot not working in (Jupyter) HTML export

[mwouts]

Prior to this, the table footer would go outside of the table when exporting the notebook to HTML

Closes #331

[github-actions]

Thank you for making this pull request.

Did you know? You can try it on Binder: .

Also, the version of ITables developed in this PR can be installed with pip:

pip install git+https://github.com/mwouts/itables.git@issue_331_fix_tfoot

(this requires nodejs, see more at Developing ITables)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.76%. Comparing base (57cf995) to head (9a92928).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #332      +/-   ##
==========================================
+ Coverage   94.69%   94.76%   +0.07%     
==========================================
  Files          24       24              
  Lines        1281     1280       -1     
==========================================
  Hits         1213     1213              
+ Misses         68       67       -1     

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