Add ability to attach multiple roles and permissions at once

This is a simple addition to the `EntrustPermission` class and the `HasRole` trait.  It gives the ability to add multiple permissions or roles at the same time using a familiar syntax.  They could be used as so:

```php
// Adding multiple permissions to a role
$baller->addPermissions([$ball_all_day, $ball_all_night]);

// Adding multiple roles to the user
$user->addRoles([$baller, $shotcaller]);
```