Show a QML dialog on KDE session exiting. There are two themes:

1. default.qml, this is a basic replacement for the current dialog. It
is not fully functional yet. I need to add the boot options (for grub2)
and work more on the GUI since the QML components I am using lack some
features used in the current dialog (QPushButton popup menu, icons on
button's right side, growing background effect on QPushButtons, label
text aligned to the right instead of to left). The dialog/shutdowndialog
borders also do not work properly, dialog's resizing still needs work
and the screen's graying out effect does not work. I guess the QML
dialog is stopping the graying out effect somehow.

2. contour.qml, this is meant to be used with Plasma Active. Contour.qml
uses larger buttons for touchscreen friendliness. For now it includes
only the lock screen, sleep and shutdown butons.

contour.qml is the default in this patch, that will change when this
branch is merged to kde-workspace master branch.