BrowsingPage: enable arrow key navigation
The CardsLayout on BrowsingPage cannot be navigated with arrow keys, only (back)tab.
This change adds arrow key navigation to all the relevant components.
The Home page with various grids mixed with regular buttons is rather complex and depends on screen size, so getting a good keyboard behavior turned out to be rather tricky and needs to handle lots of cases. Not 100% happy with how the buttons work, but it should feel mostly natural.