[workflow] fix potential destination for go back transition

[workflow] finish refactoring introduced by 021035b9a7ab for 'go back' transition: * fix SubWorkflowTransition.destination() prototype (must now take an entity as argument) * fix the change state for to give the entity to the transition's destination() method * we need a new method to draw workflow since we've no entity to give and 'go back' transition usually go back to multiple states

deprecate Transition.set_transition_permissions in favor of set_permissions (after all we know we're on a transition entity)

introduce 'go back' transition: transition without destination state will go to the state we were coming from