SpecificationSupersedingView.supersede_action() has conditional logic that should be in model code

[Guilherme Salgado]

That method has some logic to set definition_status according to the blueprint's state and the new superseded_by. That logic should be moved into model code before we can allow blueprints to be superseded over the API.

The call to updateLifecycleStatus() should also be moved to model code or, ideally, made unnecessary.