Improvements to Rack JSON serialization

* Added 'links'
* Added 'chassis'
Added possibility to retrieve one single Rack
Added Resource Class Controller
resource class db model and methods
Merge pull request #3 from mfojtik/racks_v2

Improvements to Rack JSON serialization
Merge pull request #4 from mtaylor/resource_class

Initial resource class work
Removed Blaa and Sausage models/controllers
Added Chassis representation type, some basic refactoring
Added Capacity representation to controller
More refactoring and added delete_rack()
Removed unused as_dict() method from Capacity
Do not store the 'chassis_url' when creating a Rack
Merge pull request #5 from mfojtik/cleanup

Some basic cleanup
Added Hosts list for Rack
Renamed 'Host' to 'Node'
Replaced 'node_url' with 'node_id'
Added ironic_url configuration variable
Replaced chassis_url with chassis_id
Merge pull request #7 from mfojtik/rack_hosts

Added Nodes list for Rack