Fix ordering of quizzes on plan page.

[rtibbles]

Summary

• Sorting was previously being done by the non-existent 'date-created' attribute, has been properly updated to date_created
• Also was using lodash 'sortBy' which does not allow defining a direction for ordering, this is changed to orderBy which allows specifying 'desc' for descending sorting

References

Fixes #12420

Reviewer guidance

Create a new quiz, see that it appears first!

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Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

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Reviewer checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-.pex
Windows Installer (EXE)	kolibri-0.17.0b0.dev0+git.2.g6a38b172-windows-setup-unsigned.exe
Debian Package	kolibri_0.17.0b0.dev0+git.2.g6a38b172-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.17.0b0.dev0+git.2.g6a38b172.dmg
Android Package (APK)	kolibri-0.17.0b0.dev0+git.2.g6a38b172-0.1.3-debug.apk
TAR file	kolibri-0.17.0b0.dev0+git.2.g6a38b172.tar.gz
WHL file	kolibri-0.17.0b0.dev0+git.2.g6a38b172-py2.py3-none-any.whl

[marcellamaki]

code changes + manual QA looks good