Fix functional test for CIP listing.

This accounts for the fact that we're now using an EditionFilter-like
class so we can render it just like an edition list (see commits
45cb0699a605 and 5677c011585a).
Fix field and model name changes.

* Since we're now using a version of the standard edition form, we need to
  test for fields namespaced to `edition` rather than
  `corporate_information_page`.
* We've renamed `type_id` to `corporate_information_page_type_id` to
  avoid a naming clash with the `type` attribute in Edition through
  single-table inheritance.
Add a less fragile workaround for CIP URL helpers.

The previous version relied on `edition` being available and linking to
an organisation, which wasn't always the case when creating a new page.
We now explicitly rely on a helper being available from the controller,
which is still unpleasant, but should fail more predictably and be
easier to track down.

(I still don't like this; alternative suggestions welcome.)