The current design uses 3 properties to calculate movement (horizontal/vertical
position and the viewport size) being up to the client class (e.g. ScrollWidget)
move its widgets when the position property changed.
It will allow to reuse the kinetic scrolling class with other plasmoids.
svn path=/trunk/KDE/kdelibs/; revision=1030136
ATM, it uses timers to do the animation, the idea is to use factory pattern
and implement the animation with QProperyAnimation too (using Qt 4.6).
svn path=/trunk/KDE/kdelibs/; revision=1024929
