Use local storage instead of cookies for settings

[zbynek]

Fixes #968 by not using cookies at all.

Testing done

Manually checked that changing settings and reloading the page preserves settings.
npm run test passes locally.

Submitter checklist

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• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
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• Ensure you have provided tests - that demonstrates feature works or fixes the issue