kcm modules have backgroundColor as main background color.
The new systemsettings sidebar design has viewBackgroundColor as main background color.
Through this, the kcm modules look a little misplaced to me.
With this patch, the sidebar's headers have backgroundColor as their background color, matching the background
color of kcm modules. Thus, kcm modules look a little better embedded.
This might conflict other's tastes or even conflict VDG guidelines I am not aware of. So let me know what you
think.