Migrate existing need_ids to Array field `need_ids`
Accepting multiple need ids from the view

also masking the input to be a six-digit numeric
field to make sure the input looks like a need id.
Correcting test name to reflect what it does
Added a test around GET /artefact json api
Show multiple needs on Artefacts Index page
Removing need description from artefact edit view

also, making changes to the tagged inputs to
make need id tags more prominent and
appear as a list.

removed unused `need_id_numeric?` method.
Maslow need id tags are links to the need in maslow
Updating tests to use multiple need_ids
Update cucumber features to test multiple need ids

also, marking tests that need javascript
and making them use poltergeist driver.
Bump content models to support multiple needs
Can't test multiple need ids and redirects together

multiple need ids need poltergeist driver and
because of that the redirect is being followed
leading to a Service Unavailable.
Replace tagsinput.js with tagsmanager.js

this js library is simpler and does what we
want it to. the markup it generates for tags
has a separate span for the need id which we
can use to bind click events to. tagsinput
was putting the remove link and tag content
in the same span.
Making changes to work with different JS library
Using updated version of govuk_content_models

this has nil checks for need_ids so artefacts
without need_ids don't error during validations.
Renamed artefacts need ids test helper

and moved it to the correct place.
Removing unused constant
Merge pull request #151 from alphagov/multiple-need-ids

Associate multiple need ids to an artefact