[Enhancement] Facebook auth dialog when displayed on popup mode

![facebook-auth-dialog-popup-warning](https://cloud.githubusercontent.com/assets/1357280/2750690/26e22eca-c896-11e3-82f5-44b42cabcf21.png)
Override buildAuthUrl function to refine auth dialog when on popup mode.
You need to setup auth client collection application component like:
````
'components' => [
    'authClientCollection' => [
        'class' => 'yii\authclient\Collection',
        'clients' => [
            'facebook' => [
                'class' => 'yii\authclient\clients\Facebook',
                'clientId' => 'facebook_client_id',
                'clientSecret' => 'facebook_client_secret',
                'viewOptions' => [
                    'display'=>'popup',
                ],
            ],
        ],
    ]
    ...
]
````