Rename widget tag to `Numeral'
Tweak layout
Code cleanup
Add reminder
Determine widget value from current page label rule
Add `folio-widget-page-rules-changed'

Signal updates to the page label settings by running the hook
`folio-page-label-changed-functions' with the updated page label
rule.
Update the page label rule when the widget value changes
Refactor to set the widget value from `folio-dialog-pages-widget-value'