Updates preferences are unclear

The preferences window currently looks like this:

The software updates option is hard to understand for the following reasons:

• The "To avoid charges..." text isn't the most important piece of information, yet it occupies the most prominent position, so it's distracting
• "Downloads and installs software updates in the background, when possible" has various issues:
  • The "when possible" is vague and introduces uncertainty
  • It's not clear why it says "in the background" or what this means
  • It doesn't mention that it also checks for updates
  • The "installs" part is inaccurate for system updates
• It's unclear what happens when the feature is turned off

Changing it to this would hopefully resolve these issues:

The non-essential text is moved into an inforation popover, so it doesn't distract. The radio buttons explain what happens when the feature is both on and off. It simply tells you want the feature does.

The mockup for this lives here.