Shows a list of members.

• Called by ?action=viewmembers;sa=all or ?action=viewmembers;sa=query.
• Requires the moderate_forum permission.
• Uses the view_members sub template of the ManageMembers template.
• Allows sorting on several columns.
• Handles deletion of selected members.
• Handles the search query sent by ?action=viewmembers;sa=search.