Add User#id_number attribute
Require User#id_number attribute
Allow additional MVC to be defined in lib/app

Expected location is in lib/app/models etc.
Add UserIdNumberController

Basic mechanics for updating a User’s id_number
Add form for editing User#id_number
Override _show_user_info to include ID Number
Override _signup to include ID Number
Redact User ID Numbers

When a User record is saved, create a CensorRule that redacts the
id_number attribute if an appropriate CensorRule belonging to the user does not
already exist.

Uses class_eval rather than instance_eval to enable the definition of
the update_censor_rules callback method.