Normalize signal & slot signatures in connection

Profiling shows Qt Creator spends 2% of its load time normalizing

Change-Id: I48937197efac2ea93571f616ed4e94551540bd5d
Reviewed-by: Pier Luigi Fiorini <pierluigi.fiorini@gmail.com>
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>