Use user wallpaper for dm, splashscreen and locksreen

[Davide Bettio]

Hello,

Quoting Martin Graesslin <mgraesslin at kde.org>:
> The idea to use the configured wallpaper falls short in a few ways:
> * It can only work with image, but not with animated, marble or whatever
> wallpaper plugin
Image plugin probably is the most used wallpaper plugin, so it would  
cover a lot of cases. Moreover we can save a static "screenshot" of it  
that can be displayed.

> * it cannot handle the multi screen case.
We can save a wallpaper for each screen.

> * we would need to know the activity before kactivity manager is started.
> Especially the login manager cannot know which user will log in, before the
> user logged in.
Everytime the activity is switched we can save the wallpaper path to a  
configuration file.
The login manager already knows the last user that logged in so it can  
display the right wallpaper. As soon a user is clicked or typed the  
wallpaper can be changed. In the worst case a default image should be  
displayed.

Bye,
Davide Bettio.