Some features, like the memory profiler, create huge amounts of data.
Often enough, we're not actually interested in all the data available
from the profiler and collecting it all can lead to excessive memory
consumption. This change enables us to optionally turn various aspects
of QML profiling off.

Task-number: QTBUG-41118
Change-Id: I7bb223414e24eb903124ffa6e0896af6ce974e49
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>