Fix performance regression of parent setting during QML object creation

This showed up in the profiles again: In QML we create a lot of objects
with many children and sending a child event each time is expensive. That's
why the VME didn't do that and hadn't done so in ages. This patch restores
that behavior and aspect of loading performance.

Change-Id: I5078fe330d913dc832b284aaecf031152dc80802
Reviewed-by: Lars Knoll <lars.knoll@digia.com>