Add missing nullable constraints

I had to change the factories and tests to be able to generate valid data.

Conflicts:

	app/models/organisation.rb
	db/structure.sql
	spec/models/organisation_spec.rb
Deal with shoulda failure on NOT NULL column

See https://github.com/thoughtbot/shoulda-matchers/issues/194
Specs no longer get away with null orgs

* Add an org for SiteYamlFile tests to link to
Merge pull request #109 from alphagov/not-nullable-constraints-redux

Not nullable constraints redux
All sites are sequenced now, remove that complexity
Stop pretending cic_regulator is important to tests
Prevent :site_with_default_host producing a second org
Be consistent about trait usage

We've often used a separate named factory to describe a slight deviation from a baseline object.
We should be consistent in using traits to describe these deviations from here on in.
Be consistent that http_status is a string in factories
Merge pull request #111 from alphagov/factory-fix

Fix the build/factories