[Feature Request] Add a "Last Seen" sort method for the Side Panel's sort order.

[spig0010]

This would simply be used as another type of sorting method for users in the side panel.

This wouldn't really require a UI change. All that's needed is another selection in the list of sorting methods.

Since VRCX already logs the last time you've joined a user, this could be useful to see who you haven't joined in a while, or very recently, when a user on your friends list is online. The only way to do this is by looking in the Friends List tab, then sorting by Last Seen, and scrolling through the list. It would be quicker and a little bit nicer to have it sorted and readily available and in your view already.