[kwin] Provide composited outline as QML instead of hand drawn FrameSvg

In order to get all our UI being written in QML, the Outline for
compositing is ported to QtQuick. It creates a QQmlContext and
QQmlComponent and loads the (currently hardcoded) qml file. The context
gets to properties exported: outline. The outline property allows the qml
to get the geometry it should use. The QQmlEngine is used from Scripting
thus all general scripting properties are exported (e.g. workspace).

The qml script is expected to create a QQuickWindow as it's root item
and style it.

The qml file is stored in a new qml subdirectory. The idea is that each
of the qml types we have gets an own directory there and for each
implementation there should be a further subdirectory.

Thus we have outline/plasma/ with outline being the type and plasma
being the implementation. But at the moment the script location is still
hardcoded.

REVIEW: 116123