Add bundling of shared resources

[philippjfr]

Bundle jQuery, Bootstrap and Font-Awesome once and share it across all models and templates.

Also adds various UI tests ensuring that no console errors indicating missing resources appear.

[codecov]

Codecov Report

Merging #3894 (0552659) into master (ebfce28) will decrease coverage by 8.24%.
The diff coverage is 34.82%.

@@            Coverage Diff             @@
##           master    #3894      +/-   ##
==========================================
- Coverage   83.19%   74.95%   -8.25%     
==========================================
  Files         217      222       +5     
  Lines       32529    32714     +185     
==========================================
- Hits        27064    24522    -2542     
- Misses       5465     8192    +2727     

Flag	Coverage Δ
ui-tests	?
unitexamples-tests	74.95% <34.82%> (-0.27%)	⬇️

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Impacted Files	Coverage Δ
panel/io/notifications.py	64.04% <ø> (-0.40%)	⬇️
panel/compiler.py	6.22% <5.26%> (-0.08%)	⬇️
panel/tests/ui/widgets/test_tabulator.py	9.46% <11.11%> (-89.49%)	⬇️
panel/tests/ui/template/test_fastlisttemplate.py	28.57% <14.28%> (-71.43%)	⬇️
panel/tests/ui/pane/test_plotly.py	30.69% <22.22%> (-67.14%)	⬇️
panel/tests/ui/template/test_fastgridtemplate.py	28.57% <28.57%> (ø)
panel/tests/ui/template/test_bootstraptemplate.py	29.62% <29.62%> (ø)
panel/tests/ui/template/test_materialtemplate.py	29.62% <29.62%> (ø)
panel/tests/ui/pane/test_perspective.py	46.66% <46.66%> (ø)
panel/tests/ui/pane/test_vega.py	46.66% <46.66%> (ø)
... and 36 more

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