Add method to stub api responses

Allow a need to be stubbed based on a JSON file in
the test/fixtures/needs directory.
Display information about a need in NeedsController#show

No longer redirect the 'show' action to 'edit',
instead displaying some basic information about
the need and a link to the edit form.

This tidies up the needs controller test a bit and
updates the integration tests to update a need so
they can still navigate to the edit form.
First attempt at a need view

* Create need view prototype
* Demark need in a bootstrap well at the top of the view
* Include sections for evidence, justification and impact
* Use government departmental colours as defined on
https://www.gov.uk/service-manual/user-centered-design/resources/colour-
palettes.html
* Style evidence in the GOV.UK 'big number' manner
Link to needs from need goal
Tweak markup and CSS from prototype

Wrap the need in an article div, and extract many
of the Bootstrap classes out of the markup into
better semantically named rules.
Merge remote-tracking branch 'origin/master' into view-need

Conflicts:
	test/integration/update_a_need_test.rb
Fix integration tests which weren't looking for the correct Edit button
Remove archaic .gitkeep files from the test/* directories
Initialise justifications to an empty array when nil
Access organisations in the Need model

When organisations are returned from the Need API
for a need, include them in the need and allow them
to be accessed as an array of OpenStructs.
Use a tweaked version of the need impact in the view mode

In the view mode, we want to use a slightly rephrased
form of the impact strings so that they fit into
the sentence "If GOV.UK didn't meet this need…".

To achieve this, a new helper method is added to the
need helper which converts the existing impact into
a key which is then looked up in the locale file.
Add a list of organisations at the top of the need

Display all the organisations for a need above the
goal. Each org is separated by a comma and space.
Add met when, justifications, impact and evidence fields to the need

Use the Need's attributes to populate the remaining
bits of data in the need view. 

I've added a second need fixture response to assist
testing when there are empty values returned from
the Need API.

This involves adding some new need helper methods 
to format numbers and percentages in a useful way.
Add integration test case for viewing a need which does not exist
Further need view prototyping

* Add need ID to breadcrumb
* Add a history button to header and remove revisions from foot of page
* Restyle impact statement based on GOV.UK help notice
* Include legislation and further evidence
* Rename evidence to interactions
Split recent changes into a separate page

Move recent changes from the show view to a new
page at /needs/<id>/revisions.
Change the 'evidence' column to 'interactions'

Rename the view helper 'show_evidence_column?' 
too.
Link to the history page from the header

Use a shared partial called "need_header" to display
the organisations, need goal and edit/history buttons
consistently between need views.
Add revision test data to fixture
Style tweaks to the need view

Use the 'important' icon from GOV.UK to highlight
the need's impact.