Mostly for the PDF bottom menu.
- Reorganize by topic, trying to limit the number
of widgets per panel to 4.
- Re-order some toggles from low to high ('off' then 'on').
- Show font size as number instead of a list of "Aa".
- PDF: add more font size values, and increase usable
contrast values.
- Add help_text to most PDF toggle titles.
- CRE line spacing: increase fine tuning min and max.
Also avoid zoom advice messages on book load.
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