Added a Role Doctrine entity class

This is my first ever pull request so I hope I've done this right!

Description
----------------
I recently started using BjyAuthorize with Doctrine and didn't like the fact that I had to import the schema.sql and then write a layer above that to make it possible to manage the permissions so I decided to make a Roles entity which linked to a User entity. After a bit of thought I thought others might like this too so I wrote it into the module.

Usage
---------
The usage is very simple:

Firstly you need to be using ZfcUserDoctrineORM

### Creating the entities ###

Next you will need to create your User & Role entity classes in your project entity folder.

Your User entity class must implement `BjyAuthorize\Provider\Role\ProviderInterface` and `ZfcUser\Entity\UserInterface`

Your Role entity class must implement `BjyAuthorize\Acl\HierarchicalRoleInterface`

Examples are provided as `BjyAuthorize/data/User.php.dist` and `BjyAuthorized/data/Role.php.dist`

Once you have created your entities you can set up the database with the following command

    ./vendor/bin/doctrine-module orm:schema-tool:create

### Configuring ZfcUser and BjyAuthorize ###

Next in your ZfcUser configuration specify your user entity class for the **user_entity_class** setting

Then in you bjyauthorize settings include the following 2 options:

```php
// Set to use the DoctrineEntity identity provider
'identity_provider'     => 'BjyAuthorize\Provider\Identity\ZfcUserDoctrineEntity',

// Set to use the DoctrineEntity role provider
'role_providers'        => array(
    'BjyAuthorize\Provider\Role\DoctrineEntity' => array(
        'role_entity_class' => 'FQCN TO YOUR ROLE ENTITY CLASS',
     ),
),
```

And you're configured and ready to go. All you need to do is make sure your default role is added to the database.

I hope you find this a useful addition, if it is not something you want to accept maybe I should offer it as a separate module?