Use Q_* macros.

This way we won't conflict with boosts signals and slots.

Change-Id: Ia92b283a5b47b7bc8c2bec2c6be664c9b7f1bed8
Reviewed-on: https://gerrit.libreoffice.org/6682
Reviewed-by: Tor Lillqvist <tml@collabora.com>
Tested-by: Tor Lillqvist <tml@collabora.com>