Traverse Action

We'll keep track of our hops as we process the Path_a component, populating them as we go into the metamodel.

We also set a class_cursor to track which class is currently providing the instance set to hop from.

And we initialize a string, name, which we'll use to uniquely identify our traverse action.

We check to ensure the path length has at least two hop elements, otherwise we can't hop anywhere.

Also we ensure that the destination class exists in our model.