Contact now uses Organisation, removes Department

Also changing all the tests for the models and associated bits of non-view
or controller that touch contact.

Part of https://www.pivotaltracker.com/story/show/67487248
Contacts uses Organisation in Views

Also changing all controllers, feature tests and routes
Add index for organisation_id on contact_groups
Test cleanup for using Organisations

Some tests from Master were now failing with my new Organisations tests.
This commit fixes those, namely view_contact_spec and view_contacts_spec.

Also changing how Groups are matched to Organisations in seed by doing a
find or create in seeds and removing the old call for the orgs API in env
files.
Refactor Organisation spec to test methods

As per:
https://github.com/alphagov/hmrc-contacts/pull/113#commitcomment-5908997
I've refactored this test to test the actual methods in Organisation.rb