Implement an incident-listing endpoint.

Request:

```
GET /incidents?since=1408471710
```

Response:

```json
[
  {
    "unique_id": "http://stackoverflow.com/questions/24867971/jclouds-chef-not-bootstrapping-configuring-vm",
    "original_reporter": "stackslurp",
    "url": "'http://stackoverflow.com/questions/24867971/jclouds-chef-not-bootstrapping-configuring-vm",
    "title": "JClouds-Chef not bootstrapping &amp; configuring VM",
    "tags": ["java", "chef", "jclouds"],
    "assignee": null,
    "assigned_at": null,
    "completed_at": null,
    "created_at": 1408471710,
    "updated_at": 1408471720
  }
]
```

re #24