Closes #ISSUE

Serializes the onboarding page to the database to ensure that if Zed is
closed during onboarding, re-opening Zed restores the onboarding state
and the most recently active page (Basics, Editing, etc) restored. Also
has the nice side effect of making dev a bit nicer as it removes the
need to re-open onboarding and navigate to the correct page on each
build.

Release Notes:

- N/A *or* Added/Fixed/Improved ...