Added __NAMESPACE__ to HasRoles trait and EntrustRole class to make the ...

When working with this package, I gave my models a namespace of `App\Models`.  I figured this was par for the course when working with Laravel to keep my Models from interfering with other Models.  When I tried to add roles to my user model and such, it through an error saying it couldn't find a `Role` class.  After some digging, I realized it was coded under the impression that no one would namespace their models.  I made a quick change to the relationship function in the `HasRole` trait and the `EntrustRole` Model to allow for someone to namespace their models.  This does assume that the `Role`, `Permission`, and `User` model are all in the same namespace.  However, I feel this is a safe assumption.