Removing entries in lists doesn't disconnect in graph UI

If a member object is removed from a list of references - that disconnection is not reflected in the nodal UI.

The nodal UI should monitor such disconnections and update.

Start by tracing the nodal UI's handling of list-of-reference changes and how a removed member is represented as a graph disconnection. Done means removing a member from a reference list updates the graph UI so the corresponding connection is no longer shown; the issue names no files or tests.

Written by the indexing model from the issue text.