This brings over RBCommons's list item spinners, but makes their

presence dynamic. A ListItemView subclass can now call showSpinner() to

cause a spinner element to fade in, and hideSpinner() to fade it out and

remove it.

In a ListItemView subclass in some new code, I showed the spinner before calling

an AJAX operation, and hid it after it completed. Saw the spinner fade in and then

out.