Show locked resources

This adds the `locked` attribute to a resources details for:

* Servers
* Images
* Load balancers
* SQL instances
* SQL snapshots

```
$ brightbox servers show srv-12345
INFO: client_id: cli-12345
                id: srv-12345
            status: active
            locked: false
              name:
        created_at: 2014-08-12T08:07Z
                 ...
```