Improve password complexity requirements

Add a new Passwords module, which evaluates and generates passwords.
Adapt User to use this module.

In addition to checking the length, the module verifies that a password
contains a certain number of character classes like uppercase/lowercase.
These classes can be configured in the authentication settings.

Also increase the default minimum password length from 4 to 10.
Improve password complexity cukes, add copyright
Cukes: Fix another default login password
Merge pull request #170 from opf/feature/rails3_improve_password_complexity

Improve password complexity requirements