Feature request for Union Admin Client Display

[toby]

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Summary:
Allow configurable set of columns for the Clients display.

Longer description:
When you click the clients tab in UnionAdmin, it shows the columns:
Client ID, User Account, State.

If you want to see the value of any attribute, you must view each client individually,
a see all his attributes, looking for the one you want.

This feature request is to allow an admin user to add or replace those with columns
showing the value of some client attribute.

(The same would apply to the Rooms Display as well.)


Motivation:
I am now allowing non-logged in clients to use my app.
They don't have a User Account, so for them the User Account column is --.
But I give them a temporary name, and store it in a client attribute, ClientName.
For logged-in accounts, it is the same value as User Account.

It would be most useful if I could put that in the client list display, making
it much easier to find a particular one.

But this would be useful more generally:
Suppose you had some attribute for say, activity level, and you wanted
to see the most or least active clients. You could specify that attribute
and then sort on it, to get a profile of activity on your server.