'Constructs a tab of the given type_name.
Args:
type_name (str) - the type of tab that should be constructed
**kwargs - any other keyword arguments needed for constructing this tab
Returns:
an instance of the CourseTab subclass that matches the type_name'

@classmethod
def load(cls, type_name, **kwargs):

    json_dict = kwargs.copy()
    json_dict['type'] = type_name
    return cls.from_json(json_dict)
