Better "!stats"; can display peak and current bandwidth usage.

Network stats are now updated every minute, so that we have them handy for
printing in logs, or by issuing the !stats command.

Note: this checkin disables the once-per-hour stats logging.
I do not know wether or not that is useful functionality.

src/main.c

@@ -70,7 +70,7 @@ void hub_handle_signal(int fd, short events, void* arg)
 		case SIGUSR2:
 			hub_log(log_trace, "hub_handle_signal(): caught SIGUSR2");
 			{
-				user_manager_stats(hub);
+				user_manager_print_stats(hub);
 			}
 			break;