Ipywidgets 8 support

[vidartf]

Ipywidgets 8 is above to be released, and some changes are needed to support it:

• [x] We cannot use the .extend() method from the base classes anymore. We should switch to using class ... extends pattern (switched to es2018 throughout).
• [x] We cannot use _ipython_display_ for the preview anymore. We should switch to _repr_mimebundle_.
• [x] Add serializers for non-finite floats. Closes #366.
• [x] Dropped support for Python < 3.7, including Python 2.

[codecov-commenter]

Codecov Report

Merging #378 (a7f9cca) into master (a78cb57) will decrease coverage by 0.81%. The diff coverage is 75.49%.

@@            Coverage Diff             @@
##           master     #378      +/-   ##
==========================================
- Coverage   70.86%   70.04%   -0.82%     
==========================================
  Files          23       23              
  Lines         834      888      +54     
==========================================
+ Hits          591      622      +31     
- Misses        243      266      +23     

Impacted Files	Coverage Δ
pythreejs/_base/Three.py	58.62% <14.28%> (-29.38%)	:arrow_down:
pythreejs/traits.py	86.54% <74.50%> (-4.29%)	:arrow_down:
pythreejs/_base/uniforms.py	67.44% <78.57%> (+0.77%)	:arrow_up:
pythreejs/_base/renderable.py	85.96% <100.00%> (+0.25%)	:arrow_up:
pythreejs/animation/AnimationAction.py	73.91% <100.00%> (+1.18%)	:arrow_up:
pythreejs/core/Renderer.py	81.81% <100.00%> (-0.80%)	:arrow_down:

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[vidartf]

@akaszynski Do you want to do a review / test this?

[LtAirman]

Hello vidartf,

I’m a newbie programmer working with Jupyter Notebook and pythreejs.

All 3 of my project files at https://github.com/LtAirman/ChargeFieldTopics stopped working this morning. They no longer display the pythreejs rendered scene.

Over the last few months the cell setting up the rendered scene displayed a UserWarning, due to non JSON compliant infinite values. I believe you identified the problem, involving the pythreejs orbital camera, in issues 366 and 378 which I’ve been following.

It was my impression this non-finite number problem would be corrected with the upcoming ipywidget 8 release, seeing no rendered output at all is an awful surprise. I assume it's the same issue. What do I do now?

I’d appreciate any guidance or information you might provide in this matter.

[LtAirman]

Update, happy to report my projects' pythreejs rendered outputs are now working properly.

[LtAirman]

Along with the UserWarning.