Doc redesign

[ramcdougal]

TODO:

• Review the cards on https://nrn--3732.org.readthedocs.build/en/3732/progref/index.html
• Fix the inlined math on the what is neuron page under "Cable Theory" https://nrn--3732.org.readthedocs.build/en/3732/guide/what_is_neuron.html
• Fix CVocde, NetCon, etc link on what_is_neuron.html
• Think about how to keep installation prominent on homepage (it's kind of buried in the current version, but I really like the cards)

[github-actions]

✔️ 8271727 -> artifacts URL

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.28%. Comparing base (cfd6f24) to head (219ee85).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3732      +/-   ##
==========================================
- Coverage   68.30%   68.28%   -0.02%     
==========================================
  Files         689      689              
  Lines      111033   111033              
==========================================
- Hits        75845    75823      -22     
- Misses      35188    35210      +22     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[azure-pipelines]

✔️ 219ee85 -> Azure artifacts URL

[github-actions]

✔️ 219ee85 -> artifacts URL

[nrnhines]

Just a bit of irony in that this PR is fully passing CI without yesterday's 981458f commit in master. I suppose it is conceivable that the github macos intel runner has been quietly updated.