Disable flicking on ScrollView

task-number: QTBUG-31121

We already handle MouseWheel events separately and we do
generally not want to interact with the flickable.
I don't know if we should somehow handle this differently on a
mobile device but for now it seems sensible to disable it.

Change-Id: I7dc30050efcedd8f670b3ecdc0a9915a692fd475
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>