now look and feel packages can specify a default image wallpaper.
when a new containment is created at first plasma start or at activity creation
search for a default wallpaper inthe order:
look and feel package
if fails, from the plasma theme
we are sure to find a default after it as if neither of those specify one,
the wallpaper specified by the breeze plasma theme (Next) will be used
D21225 takes care of setting the wallpaper when a lnf theme is selected by the kcm