This updates both the config forms ListItemView and the integrations

page to utilize the new djblets-o-spinner component, and to make use

of ARIA attributes to hint to screen readers that some areas of the page

are loading.
This just leaves the extensions page left using the old spinner, but

that's intentional, as that's being completely rewritten separately.

Verified that the attributes were set correctly whenever the spinner

was shown for list items, and that the integrations page had the correct

attributes and spinner as well.