They're not needed anymore, and break my build directory from time to time.
If this commit breaks your compilation, clean your build directory (or at
least the plasma and kwin subdirectories).
Defines the DecorationButton type in DecorationOptions (needs to be
re-defined due to QML limitations) and exports the buttons as a
QList<int> property (again QML limitations).
All QML files are switched from string to the new enum type.
The Plastik decoration buttons are provided by a declarative
extension plugin as the canvas drawing API would be needed to
draw these buttons. This should be changed with Qt 5.
But it's also a nice example to show how a QML based decoration
can have an extension in C++.