add missing signal is setConstraintHints

--when an applet is updating its constraintHints
a signal must be triggered in order for everyone
to be informed. This way applets we can support
applets that update their constraintHints dynamically or
based on user demand.

src/scriptengines/qml/plasmoid/appletinterface.cpp

@@ -625,7 +625,12 @@ bool AppletInterface::hideOnWindowDeactivate() const
 
 void AppletInterface::setConstraintHints(Plasma::Types::ConstraintHints hints)
 {
+    if (m_constraintHints == hints) {
+        return;
+    }
+
     m_constraintHints = hints;
+    Q_EMIT constraintHintsChanged();
 }
 
 Plasma::Types::ConstraintHints AppletInterface::constraintHints() const