Align common string modules

[nucleogenesis]

Summary

Applies to the common strings modules the pattern @rtibbles noted here where they will export a getter function as well as the mixin for the case in which one wants to just get a string not in the context of a Vue component.

Some i18n follow-up is needed in general. This pattern could be extended to some of our other string definitions files - but this will make a bit of that easier to do.

Follow-up issue: TBD

I also added documentation re: our common modules - not sure if this is any good or helpful, very much open to feedback on this.

References

Reviewer guidance

Is there room for regression I'm not seeing?

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

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

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-0.16.0.dev0_git.20220804183826.pex
Unsigned Windows installer	kolibri-0.16.0.dev0+git.20220804183826-unsigned.exe
Debian Package	kolibri_0.16.0.dev0+git.20220804183826-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.16.0.dev0+git.20220804183826-0.3.0.dmg
Source Tarball	kolibri-0.16.0.dev0+git.20220804183826.tar.gz
WHL file	kolibri-0.16.0.dev0+git.20220804183826-py2.py3-none-any.whl