jobs: Add unit tests for Job search indexer
organisation: Add basic unit tests for Person Indexer
press: Add unit tests for Press{Mention,Release} indexers

Ensuring that unpublished PRs don't make it into the (public) search
index.
press: Test that current PressMention not in list
Add stub tests for admin

At the moment, we have no custom code in our admins. Add stub test
modules so that coverage is not inaccurately reported.