The EffectData in BuiltinEffects is extended by all the data needed for
the desktop effects KCM:
* display name
* comment
* category
* video-url
* exclusive group
* internal

This information is taken directly from the desktop files.

The Built-in effects are now also resolved through the BuiltInEffects
namespace and the KServiceTypeTrader query is adjusted to only find the
scripted effects.

Unfortunately this introduces another round of adding "kwin4_effect_" to
load and save the effects correctly. This will be removed once all KCMs
are adjusted to use the new BuiltInEffects.