Add ContentModal to display resources within the context of a Custom Channel Renderer

[jonboiser]

Summary

1. Adds a ContentModal component (which is similar to ContentPage), and integrates it to the CustomContentRenderer component (which renders the custom channel's HTML5 App)
2. Adds a themeRenderer method to the window.kolibri object provided by hashi
3. Adds version getter to window.kolibri
4. Adds a themeValidator utility to sanitize themes provided by the custom channel app and, if needed, provide warnings or errors. Uses the tinycolor2 library to parse/manipulate colors.
5. Moves files to /Learn/CustomChannel for organization
6. Integrates the option added in Add KOLIBRI_ENABLE_CUSTOM_CHANNEL_NAV - default True to options.py #8025 to TopicsPage
7. Fixes an issue where updating the context query param would cause a refresh

Demo of modal with custom theme and responsive behavior

References

Fixes #7832
Fixes #7833

Reviewer guidance

1. To enable custom channels make sure to
   export KOLIBRI_ENABLE_CUSTOM_CHANNEL_NAV=True
export KOLIBRI_CENTRAL_CONTENT_BASE_URL=https://hotfixes.studio.learningequality.org
   before running the devserer
2. Download the example channel with token favim-zinul
3. Interact with the custom channel.

If possible, add a new custom channel with a different theme and see how the theme validation works.

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

[marcellamaki]

I did a code read through and looks good so far. I'm going to do another round of manual QA in the morning and one more read through tomorrow with a fresh brain, and see if I can test out some of the custom themes also. @rtibbles if you have time for a quick review also to see if I missed anything, then I can go ahead and approve after I go through the manual QA in the morning 😃

[marcellamaki]

With the version() change, this looks good to me! Nice work @jonboiser. @rtibbles is going to do one more pass to make sure I didn't miss anything, but looks like we are ready to demo tomorrow ✅ 🥳

[rtibbles]

Nothing jumped out at me during a read through.