Add Dbus call org.kde.plasmashell /PlasmaShell setWallpaper

Usage:
qdbus org.kde.plasmashell /PlasmaShell org.kde.PlasmaShell.setWallpaper "org.kde.image" "{\"Image\":\"/usr/share/wallpapers/Canopee/\"}" 0

change to slide show, with 5 seconds rotations
qdbus org.kde.plasmashell /PlasmaShell org.kde.PlasmaShell.setWallpaper "org.kde.slideshow" "{\"SlidePaths\":\"/usr/share/wallpapers/\", \"SlideInterval\": 5}" 0