Prevent publishing of publications without attachments

Allows either HTML or normal attachments.
I didn't extended this up to Publicationesque as that doesn't include HTML attachments.

https://www.pivotaltracker.com/story/show/49121005

Should look like this when you hit the button now if there's no HTML version or normal attachment:

![test no attachment - publication - admin - gov uk - chromium_013](https://f.cloud.github.com/assets/19378/968020/01c80e58-0590-11e3-8888-5fe168fad75c.png)