client1 + client2: Fix onsubmit event handler to allow submitting forms

[SmithChart]

According to the documentation
(https://lona-web.org/1.x/api-reference/views.html#post ) it should be possible to submit a <form> using POST to an interactive lona view. Without this change this fails with a
Uncaught ReferenceError: lona_window is not defined in the browser.

This change fixes the missing reference and allows to use the POST method to submit data to the view.

[fscherf]

@SmithChart: Nice! Can you add a test too?

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: +0.10% 🎉

Comparison is base (7f8ba4c) 71.81% compared to head (a684c7b) 71.92%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #462      +/-   ##
==========================================
+ Coverage   71.81%   71.92%   +0.10%     
==========================================
  Files          84       84              
  Lines        5745     5745              
  Branches     1235     1235              
==========================================
+ Hits         4126     4132       +6     
+ Misses       1339     1336       -3     
+ Partials      280      277       -3     

see 5 files with indirect coverage changes

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[SmithChart]

Since tests rely on Docker I am not sure if I can actually run the tests anywhere. I'll look into that.

[SmithChart]

@fscherf please have another look. I've added a test. But I am not sure if it should be put somewhere specific into the ordered block. From my point of this looks OK :-)

[fscherf]

@SmithChart: Nice! I refactored your test a bit (https://github.com/lona-web-org/lona/tree/fscherf/fix-post-requests)
If you ok with the changes just squash my commit into yours. Also please remove the black configuration from the pyproject.toml.
After that the PR should be mergable

[SmithChart]

@fscherf: I have squashed your suggested changes. Thanks for the update!

[fscherf]

@SmithChart: Great! Thanks for contributing!