Update Graph.update_from_editable_future_graph to more performantly delete superflous nodegroups

[chrabyrd]

This block has been added near the bottom of the function:

            with connection.cursor() as cursor:
                cursor.execute(
                    """
                    DELETE FROM node_groups
                    WHERE NOT EXISTS (
                        SELECT 1 FROM nodes WHERE nodes.nodeid = node_groups.nodegroupid
                    );
                    """
                )

It iterates the entire node_groups table and deletes "orphaned" NodeGroups -- that is, NodeGroups without a Node

This is a temporary fix, and should be replaced with a solution that only deletes NodeGroups that are related to either the source_graph or editable_future_graph.

[chrabyrd]

resolved in latest