Update API adapters.

So that we get partial matching for panopticon request body in the test
stubs.
Send updates to search after changing the topics

Also update tests to check that the correct topics are being sent to
panopticon after they're changed.
Move topic retagger test to integration directory

It's not a unit test, so it shouldn't live under test/unit
Merge pull request #1711 from alphagov/register-topic-changes-with-search

Register topic changes with search