An artefact can be associated to multiple need_ids

1. updating tests to setup correct data
2. testing that Artefact.any_in searches
within the need_ids Array for the need_id
being looked-up
3. adding need_ids to the ArtefactPresenter
4. using latest version of govuk_content_models
that provides support for multiple need_ids
Merge pull request #174 from alphagov/multiple-need-ids

An artefact can be associated to multiple need_ids