Block publishing

Depends on https://github.com/Connexions/cnx-authoring/issues/173
Rather than formatting the blockers in `block-publish.coffee`, why not leave them as an array and format them here in the template?  This way you could do something like
```
<ul>
  {{#each publishBlockers}}
    <li>{{this}}</li>
  {{/each}}
</ul>
```

Which would it appears be a more appropriate way to format the blockers, as they appear to be a list?