prefs-dialog: Drop the notebook

Replaces the GtkNotebook by a HdyColumn in a GtkScrolledWindow, making
the preferences dialog a single long column. This also sets default a
height and width so the dialog isn't ridiculously small by default.

This allows the dialog to fit in narrow screens like on a phone.
3 jobs for wip/aplazas/adaptive-preferences in 4 minutes and 40 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
failed #201532
flatpak

00:04:40

 
  Deploy
skipped #201533
review
skipped #201534
allowed to fail manual
stop_review
 
Name Stage Failure
failed
flatpak Test
Exporting org.gnome.Epiphany to repo
error: /builds/Community/Purism/epiphany/app/export/share/icons/hicolor/scalable/apps/org.gnome.Epiphany.svg is not a valid icon:
Export failed: Child process exited with code 1
Uploading artifacts...
WARNING: epiphany-git.flatpak: no matching files
_build/meson-logs/meson-log.txt: found 1 matching files
WARNING: _build/meson-logs/testlog.txt: no matching files
Uploading artifacts to coordinator... ok id=201532 responseStatus=201 Created token=bnd-4Bv4
ERROR: Job failed: exit code 1