Initial Minimum Password Strength

Hey guys,

This is a little PoC for enforcing password strength in a user profile.  This enables a config option to be set to enforce the minimum password being changed.

You will also need to edit `3rdparty` to include the following in `composer.json`:
```
        "require": {
                ......
                "bjeavons/zxcvbn-php": "*"
        }
```
And run `composer update`

My question is, is there a more modular way of doing this?

As in rather than changing core, overwrite the **ChangePassword** controller within a module/app somehow.