Handle user update events & consequential UI changes

[neiljp]

Currently we regularly get new presence information, but I believe the user information is fixed as per the start of the session.

We should implement event handling to update the user data, as well as UI changes which may be necessary promptly, ie which aren't refreshed from the updated model data on a regular basis or as needed, though we could consider updating more frequently for better representation.

[neiljp]

To clarify for future readers, this is intended to track user information outside of presence data.

[zulipbot]

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