Image cache collector supports project storage

The image cache collector project need the project storage and path cache as arguments. We have to look into life time of both. The project storage has to outlive the image cache collector.

The collector should render directly without the model.

The idea is to extend the qmlpuppet with a different mode. It gets the size and path of the Qml file, and renders the Qml file and returns an image. That would be much more robust than using the rewriter, model and node instance view.