A Resource implementation for Conductor

 * Implemented Resource class which represents a dict as an object
 * Wrapped values returned by Conductor API into Resource
 * Made DB layer return datetime objects as strings
 * Changed Conductor to support the following behaviour:
 ** For major objects (Cluster, Templates), API returns the object on
    read, create and update operations. None is returned on delete.
 ** For nested objects (Node Groups and Instances), API returns
    object ID on create. None is returned on update and delete.

Change-Id: I83d9177c778654154c550fc66061bf320de877e4
Merge "A Resource implementation for Conductor"