Make the live preview a dockable window

Currently, the live preview uses qml (.exe) to run the scene. The qml live preview debug service is taking care of the live preview functionality.

qml runs in a separate window and procces.
This means to the user it is presented as a top-level widget belonging to a different process.

Ideally, the live preview is integrated similarly to the 3D Editor.
The 3D Editor also runs in a different process but we integrate the editor using the qml2puppet. This requires forwarding events from QDS to the qml2puppet and getting back the frame buffer.

The live preview could work in nearly exactly the same way. This would require:

• The livre preview becomes a view with its own dockable widget.
  This widget can also contain the controls to control the live preview, like start, zoom etc..
• Instead of running qml(.exe) to preview the qml component we would run qml2puppet in a preview mode. We can still use the qml live preview debug service to implement the actual preview behavior. qml2puppet would have to reimplement what qml.exe does for previewing the QML.
• Events from QDS would be forwarded to the preview using the qml2puppet commands.
  The qml2puppet would send over the frame buffer with e.g. 30 frames per second for the preview. We might get performance issues and have to consider implementing a better sharing for the frame buffer. Tthe rest of the qml2puppet would benefit from this.