We have few enough pages that this makes sense over a manual window.
The page icons are fairly arbitrary, but can be changed later, or designed from scratch if necessary.

Note that we cannot use the new (in 1.5) AdwPreferencesDialog because it requires AdwWindow as a parent, and is also not a GtkWindow, which breaks some internal generics we have.

Opened Preferences, checked all tabs were there, tried a search or two.