Member list should sort by display name

The current sorting system sorts members alphabetically by their usernames, but now that we have display names that can be quite confusing.

For example, despite my display name starting with an S, since my new username starts with a dot I'm always at the top of the member list in group chats. This looks very odd, because all you'd see is the display name at first glance and it could make the member list seem a bit random if other people have similar usernames.

It'd just make more sense to sort by the username that you see users have when you look at the member list. So: server nickname > display name > username