Create emergency contact details and navigation

**This must be merged first: https://github.gds/gds/alphagov-deployment/pull/698**

Emergency contact details for GOV.UK operations need to be added to the Support app behind Signon. These used to reside behind the Government Communications Network. However, this is being closed down. The information will also be held in the government Basecamp instance in case Signon goes down.

The new feature includes a navigation link on the Support app landing page, and a new page with the contact details.

The actual phone/email/names are held in a separate `.yml` file to be included elsewhere when deployed to production.

![home - gov uk support](https://cloud.githubusercontent.com/assets/1482862/3954274/9e8b9936-26f4-11e4-95cb-455eaada3eae.png)

Clicking the new link takes the user to the emergency-contact-details page

![emergency contact details - gov uk support 1](https://cloud.githubusercontent.com/assets/1482862/3954290/bd09c8f6-26f4-11e4-8269-114a025d35d5.png)

The page contains the required emergency contact routes for four primary emergency categories, and secondary contact details in case the primary ones are not contactable.

I paired with @benilovj on this.