due to plasma change, shadow is not included by default, hence kwin
tabbox need to handle shadow by itself, and due to kwin is compositor
and have shadow as effects, it's not a good idea to use X property to
pass shadow from kwin to X and to kwin. This change use the old way to
draw shadow side the tabbox, and partly move the blur region setting to
qml.
REVIEW: 108243
A new service type is introduced which is used by the KCM to find
all available window switcher layouts. This makes it finally possible
to have 3rd party window switchers.
Also the tabbox finds the packaged QML file through the service
definitions.
Desktop switcher is not yet in packaged version (UI to configure
is missing).
REVIEW: 103951