Allow never published manual documents to be deleted through the UI

Opened for discussion. TODO:

- [ ] Unpendingize cucumber tests (I thought I'd done them. Guess not).

I figure it's worth having the wider discussion about wether we want to do this and what protections we want to add round this before going any further.

Add a delete button which only displays for Manual Documents that have never been published.

This also guards against deletion of published documents, showing a flash message if so. However, the button isn't shown in this case so that error shouldn't be encountered.

This will delete the manual document entirely -- without confirmation at the moment. Attempting to use 'confirm: true' on a button asks for confirmation but doesn't continue if the user chooses OK -- also alerts twice. The rails ujs isn't attaching properly or it'd work.