Active model serializer

Not sure if we want to merge this in yet, but these changes customize the JSON serialization to have Instances return Endpoints. So when you get a resource like `/services/1/instances/1`, you get:

```
{
    "description": null,
    "endpoints": [
        {
            "created_at": "2014-06-09T20:24:13.396Z",
            "description": "WESB mediation to version 4",
            "endpoint_type": "WESB mediation",
            "id": 2,
            "instance_id": 1,
            "name": "Development.WESB.commutedValueService4",
            "updated_at": "2014-06-09T20:24:13.410Z",
            "url": "http://indy:8889/gateway2MediationWeb/sca/gateway2Export_WS_SOAP11/cvws4"
        },
        {
            "created_at": "2014-06-09T20:24:13.389Z",
            "description": "Direct endpoint to version 4",
            "endpoint_type": "Direct",
            "id": 1,
            "instance_id": 1,
            "name": "commutedValueService4",
            "updated_at": "2014-06-09T20:24:13.408Z",
            "url": "http://ihswasdev/CommutedValueWS400/CommutedValueService"
        }
    ],
    "id": 1,
    "name": "Commuted Value Service 4",
    "version_of_artifact": "4.0.0 [2013-11-05 18:26:00 EST]"
}
```

So we can leave this branch up here to demonstrate how Active Model Serializer works.

/cc @melima @nasimoyz