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.

Before:
![screen shot 2014-09-11 at 14 13 37](https://cloud.githubusercontent.com/assets/355033/4250236/4b3b028a-3a81-11e4-918d-d72e642bc58e.png)

After:

![screen shot 2014-09-12 at 14 33 48](https://cloud.githubusercontent.com/assets/355033/4250255/7769e484-3a81-11e4-8699-453f2557e5c1.png)


It's drawing a box around CNAMEs this way too:
![screen shot 2014-09-15 at 11 15 42](https://cloud.githubusercontent.com/assets/93739/4269828/60938c6e-3cc1-11e4-9f06-b2353ade57a6.png)

I found that if I added a `span`, and applied the `breakable` class to it instead of the `td`, then it solved the problem. Given that, we should be able to remove the complexity of the conditional.