Add none option for /who

Fixes https://github.com/profanity-im/profanity/issues/1425
`/who none` now displays all users in an muc without an affiliation

src/command/cmd_ac.c

@@ -627,6 +627,7 @@ cmd_ac_init(void)
     autocomplete_add(who_room_ac, "owner");
     autocomplete_add(who_room_ac, "admin");
     autocomplete_add(who_room_ac, "member");
+    autocomplete_add(who_room_ac, "none");
 
     bookmark_ac = autocomplete_new();
     autocomplete_add(bookmark_ac, "list");