[Screensaver] Functionality to add new screensavers

[alex5imon]

It is possible to create screensavers with Pi3D for example.

kano-settings needs to give you an easy way to add your own screensaver. To enable the screensaver you just need to change this line: https://github.com/KanoComputing/kano-desktop/blob/master/kdesk/.kdeskrc#L29

Here is a user looking for a simple solution to this approach: http://world.kano.me/forum/topic/pi3d-screensaver