Populates the custom columns we added to the posts table in the dashboard.
Change the dashboard post query to sort based on a custom column we added.
Declares which of our custom columns on the list of posts are sortable.
Handle the ORDER BY on the vehicle list (edit.php) when sorting by photo count.
Enhances the list of vehicle posts in the dashboard.
Adds slugs to the post table columns array so the dashboard list of vehicles is more informative than the vanilla list for posts.