Use user wallpaper for dm, splashscreen and locksreen

[Davide Bettio]

Hello,

During boot process background is changed several times, to avoid this  
I think that current activity wallpaper should be used as  background  
for display manager, splashscreen and lockscreen.
To get this feature working we just need to save current wallpaper to  
a configuration file every time current activity is changed.

Any comment?

Bye,
Davide Bettio.