Adds the Mandrill adapter.
New class method Email.process to process a collection of inbound emails.
Added a 'check' route and action, because Mandrill does a HEAD request at the endpoint to check if it's valid before letting a user add it.
Process the array of params in the controller
Mandrill adapter returns an array of reciepients
Remove the check route required by Mandrill.
update feature test to account for normalized_params possibly being an array