Flask application initialization.

def init_app(self, app,
                 entry_point_group='invenio_workflows.workflows',
                 **kwargs):
        """Flask application initialization."""
        app.config.setdefault(
            "WORKFLOWS_OBJECT_CLASS",
            "invenio_workflows.api.WorkflowObject"
        )
        state = _WorkflowState(
            app, entry_point_group=entry_point_group, **kwargs
        )
        app.extensions['invenio-workflows'] = state
        return state