Delete artefacts when changed to nonindexed kinds

We have had some artefacts created (incorrectly) as Answers when they should
have been CompletedTransactions. These were not removed automatically. This
change would ensure that they are in future.
Small readability changes
Add tests for Search update observer
Remove bogus file
Merge pull request #57 from alphagov/remove_nonindexed_artefacts_when_changing_kind

Delete artefacts from search index when changed to nonindexed kinds
Fix incorrect artefact kinds

Publisher hasn't been correctly updating the kind when a (new) edition is
published with a different kind (format).
Merge pull request #58 from alphagov/fix_incorrect_artefact_kinds

Fix incorrect artefact kinds
Move and rename the search indexing test.

Because it relies on the search observer, which is defined on the
ActionDispatch class, it fails at the unit test level.