Refactor pill and add tests

[weeman1337]

Preparation for further work on permalinks / pills.

• Pill now does only the view part
• Adds usePermalink hook for the logic
• Cover pill with tests

Checklist

• Tests written for new code (and old code if feasible)
• Linter and other CI checks pass
• Sign-off given on the changes (see CONTRIBUTING.md)

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This change is marked as an internal change (Task), so will not be included in the changelog.

[andybalaam]

Fantastic, thank you!