create_admin checks password against regexp
add external config check to changes_password
full integration with config/admin.yml

Admin now has a before_save callback that writes its username and
password to admin.yml so that if you change your password on the Change
Password page your new password isn't lost at the end of your session.
Also add Before and After hooks to Cucumber that set the contents of
admin.yml back to what they were before the tests were run.

Also, improve create_admin by adding exit codes and the ability to stop
the program prematurely by typing "exit" or "quit" (case insensitive).
The tests reflect this.