Fix underlying bug whereby duplicate draft sections (and possibly manuals?) can be incorrectly created in database

[floehopper]

This follows on from Check or remove delete_documents_marked_for_delete, delete_duplicate_drafts & find_duplicate_documents scripts.

Reading the note for the commit where the code for the delete_duplicate_drafts rake task was introduced, it's clear this script is working around an underlying problem in the application where a new draft is rejected by the Publishing API, but still saved to the local database.

Similarly the note for the commit where the code for the delete_sections_marked_for_delete rake task was introduced, it's clear that this script is dealing with a workaround which editors have been using for the same problem.

Similarly the note for the commit where the code for the find_duplicate_documents rake task was introduced, talks about an underlying bug.

We should fix the underlying problem so we can remove these scripts!

I also notice that there is a chunk of duplication between these three rake tasks in finding the duplicates.

[floehopper]

I notice that the update actions for both manual and section result in the relevant models being saved to the local database before they are sent to the Publishing API:

• Manual::UpdateService#call
• Section::UpdateService#call

I imagine fixing the underlying problem will mean only saving models to the database if the calls to the Publishing API return successfully - whatever that means.

[chrisroos]

I've added issue #1120 to capture the problem experienced when creating multiple manuals with the same title. That might be related to this issue.