This seems to be the key point for many of the unexplainable crashes
that we've been seeing all over the place, especially in the KDED module.
When the ConfigMonitor is updating the properties one by one, the
change signals are being emitted immediatelly. So if someone is listening
to these signals, and will try to access some property that we have not
udpated yet, they will get inconsistent data (like empty mode list for
instance), leading to crashes.

With this patch we block signals emission on the output, collect all changes
that happened, and then emit the signals all at once after we updated all
the properties. This way applications can safely access any properties.