The Hello GL2 Example was using the older Signal/Slot syntax that made
use of the macros `SIGNAL()` and `SLOT()`. I changed it to the newer
one.
Change-Id: I8e55015383847a04b07f751fe9fc94b81956a896
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>