Fix bug 1012899: Update homepage with operator / manufacturer buttons.

This isn't quite complete; still waiting on confirmation of what text to use for the Maintain section link, and for whether we want to hide the maintain section or not.

This makes a few stylistic changes to make the homepage match the mockup from [bug 1014688](https://bugzilla.mozilla.org/show_bug.cgi?id=1014688) as well as adding two buttons that reveal different CTAs when selected.
Assuming this element should just span the full width, you don't really need to declare its column span at all. Or you can use <code>.span-all()</code> to explicitly override a span declared elsewhere.