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Fixed problem with rearranging `$:/tags/PageControls/`
Docs update

Added a link to @giffmex’s Bible study notebook, and updated the link
to Ton’s guide to building top menus and toolbars.
Merge pull request #248 from davidjade/master

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Resolve conflict
Fallback to a list of default themes

Avoids the situation where an empty wiki uses the vanilla theme unless
you explicitly apply a different theme.