Fix JSON response for status API to include user information and fix 500 error

I've fixed several 500 errors regarding status json API. Here's a sample output for a single status. Let me know what you think.

```json
{
    "content": "Here's a status....",
    "created_at": "2014-04-12T11:12:13.463Z",
    "updated_at": "2014-04-12T11:12:13.463Z",
    "user": {
        "id": 1,
        "username": "rcdilorenzo"
    }
}
```