Fix for ManualDocuments Preview not working

We were missing an action which wasn't needed until some previous
refactoring changed how the Preview worked. I've added some tests to
make sure this doesn't happen again along with adding a service for
previewing manual documents.
Merge pull request #109 from alphagov/fix-manual-document-previewing

Fix for ManualDocuments Preview not working
Merge pull request #108 from alphagov/refactor-cma-cases

Specialist documents and CMA case refactor
Remove unused code as reported by SimpleCov
Merge pull request #110 from alphagov/remove-unused-code

Remove unused code as reported by SimpleCov
Change notes for manual sections