Effects can provide support information through properties

The supportInformation is extended to also read the properties
on all effects. In addition each effect can be queried just for
itself through D-Bus, e.g.:
qdbus org.kde.kwin /KWin supportInformationForEffect kwin4_effect_blur

All effects are extended to provide their configured and read
settings through properties. In some cases also important
runtime information is exposed.

REVIEW: 105977
BUG: 305338
FIXED-IN: 4.9.1