Improve the styling of the repository confirmation banners.

The repository confirmation banners (cert/SSH key confirmations), plus
the public SSH key display, were ugly in the new UI. They appeared as
rounded things just kind of stuck there in the form.

This change blends them in much nicer, making them actually feel like
part of the form.

While I was at it, I also improved the SSH key display by adding the key
type at the beginning (which services like GitHub require).

Checked each banner type. They all looked fine.