Don't break configuration when saving layouts

Plasma::Applet::config() returns a "/Configuration" group, but the
dumpCurrentLayoutJS DBus method saves all applets' config from root,
so when we need to save some value through scripting api it will
always prepend "/Configuration"

shell/shellcorona.cpp

@@ -550,6 +550,8 @@ QByteArray ShellCorona::dumpCurrentLayoutJS() const
 
                 QJsonObject appletJson;
 
+                appletConfig = KConfigGroup(&appletConfig, QStringLiteral("Configuration"));
+
                 appletJson.insert("plugin", pluginName);
                 appletJson.insert("config", dumpconfigGroupJS(appletConfig));