Add async job to deliver admin contact emails
Add contact form object

Email regex taken from the Rails docs:

http://apidock.com/rails/ActiveModel/Validations/ClassMethods/validates_format_of
Add controller action to queue contact email job
Merge pull request #18 from moneyadviceservice/contact-email-api

Contact email API
Adds a "Principal" model.

Includes an `identifier_token` attribute to be used during authentication.
Adds `factory_girl_rails` for model factories.
Introduces a simple error page.
Generates the token when a Principal is created.
Introduces token auth in a before action hook.

`before_action :authenticate` expected to be overridden for controllers needing finer-grained control over authentication.
Excludes certain pages from authentication.

Specifically error, pre-qualification and identification pages.
Adds page objects for home and error pages.
Adds a bare-bones factory for the "Principal" model.
Simple feature spec for token authentication.