Monolithic commit re-factors OrganisationType and adds a Devolved Administration type.

• OrganisationType replaced with a static (non-database) model
• OrganisationType related stuff extracted from Organisation into a separate concern.
• OrganisationsController#index cleaned up - all organisations are retrieved with a single query and logic for grouping moved into a new OrganisationsIndexPresenter.
• Lots of updated tests.# This is a combination of 3 commits.
Migration to add new devolved administration organisations.
OrganisationType agency_or_public_body and non_departmental_public_body are now model attributes.
Bring #some# sanity to organisations/index view.
Added devolved administrations to organisations index view.
Validating that devolved administrations are govuk_status exempt.
Resolved merge conflict missed while rebasing.
Trailing new lines
Fixed broken test - added a valid devolved_administration factory
Oh the EOF newlines
Organisations index was doing #something# with translations.  Now it isn't.
Fix Lancaster House contact info.
Sort policies by reverse chronological.
Add ability to update org shots from a slug file.
Update organisation screenshots as per 48941633.
Split migration to cope with live deployment.
Merge pull request #850 from alphagov/update-organisation-screenshots

Update organisation screenshots

https://www.pivotaltracker.com/story/show/48941633
Merge pull request #847 from alphagov/fix-lancaster-house-contact-info

Fix Lancaster House contact info.

https://www.pivotaltracker.com/story/show/56865632
Merge pull request #849 from alphagov/fix-policy-sort-order

Sort policies by reverse chronological.

https://www.pivotaltracker.com/story/show/47438583
Merge pull request #838 from alphagov/add-devolved-administration-org-type

Add devolved administration org type

https://www.pivotaltracker.com/story/show/44877183