Versioned objects support for Nailgun DB

In order to ensure *automated* upgrades/updates & downgrades/rollbacks rolling for Fuel master node as well as for Mirantis Openstack installations, provide the versioned objects support for Fuel environments and Mirantis Openstack configurations in Nailgun DB.

The idea is to use a finite machine style approach while designing a complex upgrade (updates & downgrades/rollbacks) stateful scripts which should communicate with Nailgun API to put and get its state and make a decisions based on its current state. Such an approach ensures postponing of any 'rolling' actions for offline nodes as well.

Nailgun side should provide enough versioning info for all affected objects and any other DB entities involved.

As a ref, please see the Nova unified object model as well https://blueprints.launchpad.net/nova/+spec/unified-object-model.