Oxygen::ShadowCache::shadowSize() now returns the shadow extend outside of the window body (the extend)
Overlab between the actual shadow pixmap and the window body is dealt with internally (by creating larger pixmaps)
This allows notably Oxygen::Client to not attempt to draw shadow when shadowSize == 0 (which was never the case
before)
The flag has been made obsolete by the fact that window corners are not part of the shadow anymore.
Configuration::useOxygenShadows is now dealt with by setting the active flag directly.
