Fix fatality notice casualty field duplication

www.agileplannerapp.com/boards/173808/cards/8196

this issue seems to have its roots in this refactoring:
https://github.com/alphagov/whitehall/commit/3b8145

the remove button handler script adds an additional
hidden field '_destroy' to the form with value true,
which should be sent to the server, which was not
the case. instead this extra hidden field was being
sent to the server.
Make org slug changer commit routes.

Without this, the redirect won't be live until something else commits
the routes.  There's no guarantee on when that will happen.
Extract "exports to publishing api" into mixin.
Add content_id to world locations.
Migration to populate world_location content_ids.
Generic presenter for non-edition placeholders.
Make World Locations publish to publishing API.
Use specific type in placeholder format name.
Send all world locations to content store.
Add world_locations to case_study publisher.
Fix broken tests.
Move concern from models to lib directory
Merge pull request #1871 from alphagov/org_slug_change_commit_routes

Make organisation slug changer commit routes.
Go through presenter finding method in tests

This decouples the logic for deciding the appropriate presenter for a given
model out of the tests.
Rename ExportsToPublishingApi module

"Export" isn't the verb word; "Publish" is more appropriate.
Abstract away calls to the Publishing API

Instead of invoking workers directly when publishing models to the Publishing
API, app code should go through this abstracted interface. This keeps the logic
for deciding how any given model should be represented in the content store
(and how it gets there) in one place.
Merge pull request #1878 from alphagov/world-location-placeholders

Add world locations to content store
Delete erroneously synced users

Signon push update rake task pushed information
of users who had never used Publisher, so cleaning
that up. see related:

https://github.com/alphagov/signonotron2/pull/290/files
Merge pull request #1862 from alphagov/fix-casualty-fields-duplication

Fix casualty fields duplication
Merge pull request #1882 from alphagov/fix-erroneously-synced-users

Delete erroneously synced users