Save Information about The Deployment in The Database

For cases of LCM we need to save the deployment information(serialised cluster and node attributes) in database for each deployment.

In first implementation this information can be added to task object as "blob".

The task serialisers should be reworked to operate with serialised cluster info instead of work with nailgun database. This will help us to move orchestrator from nailgun to separate module and isolate logic of task serialiser from nailgun.

Because we need current and previous deployment info, the tasks workflow should be modified, there should not be API to manually remove any task, instead we should have background process to remove old tasks. All logic in UI that is related to manually removing tasks should be reworked.