Connection / event handler cleanup

[bmingles]

It would be good to do a general pass at making sure things get properly cleaned up in the extension

• Connections - I've observed some scenarios where the treeview can get in a state where connections are shown that are no longer active. In some cases, it is then impossible to reconnect, or clear them. This is likely a symptom of needing better disconnect / cleanup handling in the extension and needing to clear caches when connections are no longer valid. As the general connection functionality settles, we should do a pass to identify / fix any such places.