Support Nested/Recursive Object Validations

This allows for Objects to reference other objects's schemas for use
by JSON-Schema validations. Lookups are performed via the Object
Registry using a pseudo URI scheme of "obj://" e.g.

    '$ref': 'obj://TestObject#/'

Is a JSON-Schema reference, pointing towards the root of the Schema
generated for the "TestObject" object.

Change-Id: Id35c38536eb0d21bb66d3ca720d18e7f6ee733b5
Blueprint: validation-cleanup
Merge "Support Nested/Recursive Object Validations"