Live update full names for senders in the message pane.

Note that this only works for people who are currently logged in.
Folks that log in after you may pick up the old full name from
the message.  (I'll address this in a separate commit.)

static/js/message_live_update.js

@@ -8,6 +8,12 @@ exports.update_stream_name = function (stream_id, new_name) {
     });
 };
 
+exports.update_user_full_name = function (user_id, full_name) {
+    _.each([home_msg_list, current_msg_list, message_list.all], function (list) {
+        list.update_user_full_name(user_id, full_name);
+    });
+};
+
 exports.update_avatar = function (person) {
     var sent_by_me = people.is_my_user_id(person.user_id);
     var url = person.avatar_url;