effects/slide: Remove SlideDocks option
SlideDocks option was added after receiving negative feedback about sliding docks. SlideBackground option was added to provide smooth transition path for old users.
In hindsight, adding SlideDocks option was a mistake. It provides excessive configurability in exchange for more code complexity.
With the SlideDocks option removed, the docks will be static when the animation is active.
Edited by Vlad Zahorodnii