KCoreAddons qml plugins

[Aleix Pol]

Hi,
I would like to move KCoreAddons qml plugin into KCoreAddons. Now it's
KDeclarative where we are dumping all QML plugins.

I think it's a good idea because:
- it simplifies usage  the plugins for such frameworks (kcoreaddons is
not the only one).
- it ensures the code related to a feature is together.
- it keeps the documentation together.
- we don't force unwanted dependencies [1].

The only downside I see, is that KCoreAddons will end up depending on
QtQml. I think we can make it an optional if that's a problem on some
setups.

This is already done by many frameworks, such as: baloo, kactivities,
solid, phonon, krunner.

Aleix

[1] http://api.kde.org/frameworks-api/frameworks5-apidocs/kdeclarative/html/kdeclarative-dependencies.html