Methods added to the Model to map from row index to the backend
identifier and vice versa. That way the Compositing object can do
all the saving and loading.
* all properties extended to be writable and emit change signals
* contains load from and save to config functionality
* Compositing object in qml view is connected to the values of the
components. So changes are directly mapped from UI to business logic
We have an Apply and OK button in the KCModule, so we don't need one
in the view. A change signal is introduced and passed from the individual
items upwards, so that we can connect to it from the C++ side.
Only ONE of the following effects can be active at the same
time.
*kwin4_effect_slideEnabled
*kwin4_effect_cubeslideEnabled
*kwin4_effect_fadedesktopEnabled
