Fix access limited being switched on for policy

Caused by what appears to be a typo that was casting the array to a
string.
Ensure accessible attachments stay that way

The checkbox was not getting picked up by the `children` call because
it was embedded in the label tag.
Merge pull request #633 from alphagov/fix-access-limiting

Fix access limited being switched on for policy papers
Merge pull request #634 from alphagov/accessible-attachments

Ensure accessible attachments stay that way

https://www.pivotaltracker.com/story/show/49657127