Initial import of the Rack model

Note, this is just an initial import of files/classes etc to exercise DB model and controller creation.

With this patch you can do:

```
$ curl -X POST -d '{ "name": "test_rack" }' -H 'Accept: application/json' -H 'Content-Type: application/json' http://0.0.0.0:6385/v1/racks
```

And then retrieve the list of racks:

$ curl -X GET -H 'Accept: application/json' http://0.0.0.0:6385/v1/racks