Move UI translations from content packs to repository

[benjaoming]

Summary

Taking over from #5524

TODO

If not all TODOs are marked, this PR is considered WIP (work in progress)

• Has documentation been written/updated?
• Have you written release notes for the upcoming release?

Reviewer guidance

This should remove all translation files from content packs, instead fetching them from CrowdIn.

Issues addressed

#5518

[codecov]

Codecov Report

Merging #5537 into 0.17.x will increase coverage by 0.11%.
The diff coverage is 15.15%.

@@            Coverage Diff             @@
##           0.17.x    #5537      +/-   ##
==========================================
+ Coverage   62.59%   62.71%   +0.11%     
==========================================
  Files         117      117              
  Lines        6556     6550       -6     
==========================================
+ Hits         4104     4108       +4     
+ Misses       2452     2442      -10

Impacted Files	Coverage Δ
kalite/i18n/management/commands/makemessages.py	95.83% <ø> (ø)	⬆️
...nagement/commands/setup_in_context_translations.py	0% <0%> (ø)	⬆️
...tributed/management/commands/contentpackchecker.py	0% <0%> (ø)	⬆️
kalite/i18n/base.py	55.15% <10.52%> (-0.7%)	⬇️
kalite/legacy/i18n_settings.py	86.36% <100%> (ø)	⬆️
...ributed/management/commands/retrievecontentpack.py	51.48% <11.11%> (+3.3%)	⬆️
kalite/project/settings/base.py	87.38% <0%> (-0.69%)	⬇️
kalite/distributed/views.py	78.65% <0%> (ø)	⬆️
kalite/facility/api_views.py	64% <0%> (+10%)	⬆️

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[benjaoming]

This refactor isn't possible to do in 0.17 and if anyone would wanna refactor this codebase, this would be a drop in the ocean :)