Allow the CNAME to display on multiple lines

- Long CNAMEs like
  `redirector-cdn-ssl-businesslink.production.govuk.service.gov.uk` were
  causing the configuration table on the site dashboard to stretch
  beyond the margins of the container box. It's unlikely that we'll ever
  get this with IP addresses, but apply the breaking to everything in
  that `<td>` anyway.
Merge pull request #402 from alphagov/wrap_cname_on_site_dashboard

Allow the CNAME to display on multiple lines