Changes: Mention new extended_keys semantincs in layout documentation
Changes: Mention new extended_keys semantincs in layout documentation

RevBy: Jan Arne Petersen

develersrl/maliit-demo-qml,RHawkeyed/plugins,RHawkeyed/plugins,KDE/plasma-maliit-plugins,develersrl/maliit-demo-qml,RHawkeyed/plugins,KDE/plasma-maliit-plugins,maliit/plugins,develersrl/maliit-demo-qml,maliit/plugins,RHawkeyed/plugins,RHawkeyed/plugins,KDE/plasma-maliit-plugins,maliit/plugins,maliit/plugins,develersrl/maliit-demo-qml,KDE/plasma-maliit-plugins