Map filter

This filter maps input values according to a pre-registered mapping:
```js
angular.module('super-module', ['ev-fdm'])
    .config(function(mapFilterProvider) {
        mapFilterProvider.registerMapping('orderStatus', {
            'validated': 'Commande validée',
            'shipped': 'Commande expédiée',
            'delivered': 'Commande reçue'
        });

        // Optional, a default value can be defined
        mapFilterProvider.registerDefault('orderStatus', 'État inconnu');
    })
;
```

Should'nt it be something like: 
```js 
case typeof mapping === 'string' && hasOwnProp.call(defaults, mapping):
    return defaults[mapping]
``` 
?