Don't call blockSignals, but instead, to avoid an infinite signal chain,
check KCoreConfigSkeleton::configChanged wasn't emitted by ourselves writing on the
config.
Plasma::Applet::configChanged() slot was never invoked when config was written from
QML, which is wrong.

Config still loads, plasma which makes heavy use of this still loads and saves
configs correctly, no infinite signal/slot recursions.
Now if somebody connects to KCoreConfigSkeleton::configChanged from outside of
this class, it wil lreceive correct signals when somebody writes to the config from
QML.