partially filled alternate address validation
Merge pull request #339 from ministryofjustice/alternate_address_validation

partially filled alternate address validation
Start of the 'Contact Us' page implementation
Added the model for user callbacks
Renamed to UserCallback

Renamed model, view & controller from Contact to more descriptive
UserCallback.
Callback requests almost done

The only thing that's outstanding is the way to properly send the custom
data to Zendesk. The reason I didn't implement that is because I don't
have access to our Zendesk instance. Once that's sorted, I'll be able
create required custom fields, where the callback requests will be
stored.
Implemented 'Callback request' for Zendesk
Added descriptive callback message

Added the message to make it really obvious to the staff dealing with
the ticket that the user is requiring digital assistance and that (s)he
should be called.
Modified the Zendesk message

The message that will be shown to the call centre staff has been
reformatted.
The tickets are created by a callback group

The tickets are all created by civil_claims_accelerated_callback group,
so that they can be automatically assigned to the Callback Agent in
Zendesk.
Copy updates for Callback request
Updated the callback URL according to the copy

Discussed it with Eliot and updated the URL to the callback request as
per the page title.
Phone number validation for UserCallback model

Check that the phone numbers supplied:
  - are not blank
  - can contain hyphens
  - can contain spaces
Further copy changes for AD callback feature
Specified the callback route with explicitly

Gave it a friendlier name
header links
Abbreviated the path to callback page