Honor Kiosk settings in desktop configuration module.

Honor Kiosk settings:
* Fill in all desktop names right at the start of the module, using
* The name from the XConfig if set.
* The name from kwinrc if set (this happens when fewer desktops are set up as there are names in the configuration).
* "Desktop X" as a fallback.
* Block change of desktop names that are marked as immutable in kwinrc.