Feature bootstrap 3

@sandeepone Please see the way that I used to define the icons class. I think this code is necessary to transfer from the view.

Screenshot:
![login-widget](https://f.cloud.github.com/assets/1256298/1558709/99edad6a-4fa4-11e3-9482-5870cbdffab7.png)

Maybe it makes sense to add another configuration parameter for oauth? 
For example:
```php
  'twitter' => array(
    'key' => 'your consumer key',
    'secret' => 'your consumer secret',
    'icon' => fa-twitter'
  ),
```

And use some helper: ` string OAuth::icon( string $provider );`
I'm not sure ... Please see code