Validates the workflow steps from ``start`` to ``end``, inclusive.

        Returns a dict describing the validation state of the workflow.

def validate_steps(self, request, workflow, start, end):
        """Validates the workflow steps from ``start`` to ``end``, inclusive.

        Returns a dict describing the validation state of the workflow.
        """
        errors = {}
        for step in workflow.steps[start:end + 1]:
            if not step.action.is_valid():
                errors[step.slug] = dict(
                    (field, [six.text_type(error) for error in errors])
                    for (field, errors) in step.action.errors.items())
        return {
            'has_errors': bool(errors),
            'workflow_slug': workflow.slug,
            'errors': errors,
        }