* Add custom message for inclusion validation to include the allowed values.
* Force user to choose document_type from select lik the one shown at verification form.
* Convert stored document_type to a human readable text
I had mixed feelings about this rule, since I like spaces where
possible.
However, I changed my mind when I realized writing `->(thing) { }` was
similar to defining a method, and we don't have a space before the
parenthesis when defining a method.
* Create admin controller and routes
* Add pagination
* Add search by document_number
* Add EN and ES translations
* Add index specs
* Add missing model specs
