add ability for "default Model" to resource

add ability for "default Model"  on $resource so you can do nice think like that: 

```javascript
.factory('User',function($resource){
        var model = {
                contacts:[],
                logos:[]
        };
        var User = $resource('user/:id/:action',{id:'@_id'},model,{
            get: { method:'GET',   params:{action:''} },
            remove:{ method:'GET', params:{action:'remove'} },
            save:{ method:'POST',  params:{action:'' } },
            list:{ method:'GET',  params:{action:'list'},isArray:true) }
        });

        return User;

});

function ctrl($scope,User){
  $scope.user = new User()
}

/*
$scope.user = {
      contacts:[],
      logos:[]
      $get:function,
      $remove:function
      $save:function,
      $list:function
 }
*/
```

so your controller not throw exception when you try to add something to array that not exsist