Enable multiple deployments via deployment payloads

This requires you to use the [deployments API][1] and specify environment configurations via the payload. To take advantage of it, it looks like this.

```json
"payload": {
  "name": "camo",
  "config": {
    "opsworks": {
      "production": {
        "app_id": "<app_id>",
        "stack_id": "<stack_id>"
      },
      "staging": {
        "app_id": "<staging_app_id>",
        "stack_id": "<staging_stack_id>"
      }
    }
  }
},
```

This coincides with the way [hubot-deploy](https://github.com/atmos/hubot-deploy) is creating things with payloads. 

@jansiwy Will something like this approach work for your desire to have multiple installations?

[1]: https://developer.github.com/v3/repos/deployments/#create-a-deployment