What would you like to be added:
When a workflow object is created the object should be populated with the default values indicated in the specification if no value is provided.

For example, the following operation

    workflow = Workflow(
        id_="greeting",
        name="Greeting Workflow",
        description="Greet Someone",
        version='1.0',
        specVersion='0.8',
        start="Greet",
        states=[
        ],
        functions=[
        ]
    )

should create a workflow object with default values like expressionLang

        self.assertEqual("jq", self.workflow.expressionLang)

when the workflow is serialized to json or yaml, the default values should be removed if they have been populated by the sdk.

Why is this needed: