New map filter

This filter maps input values according to a pre-registered mapping:
```
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');
    })
;
```
Accept raw object in map filter
Fix default value fallback
Merge pull request #61 from Evaneos/map-filter

Map filter