ShowDesktop: Use the new DBus API for showing the desktop
This unifies the code paths (underneath KWindowSystem goes through two separate code paths) and generally makes the code a lot more direct instead of going through a bunch of layers. Additionally, it allows the KWin-side of things to check if the caller disappears and quit the "show desktop" mode if that happens.
Depends on kwin!2663 (merged)
Edited by Arjen Hiemstra