* Introducing SliceExtractor::onEvent() to handle mouse events and generate point scribbles from it, which are then published using the s_scribblePainted signal
* Implemented SliceExtractor being able to render geometry in the slice space (with correct clipping)
* Implemented creating and handling of scribbles in VolumeExplorer in cooperation with the SliceExtractor. Therefore, mouse events are passed to the SliceExtractor, the VolumeExplorer takes care of assembling the scribbles into proper geometry, which is finally rendered by the SliceExtractor. The scribbling can be optionally turned on using the VolumeExplorer::p_enableSclibbling property.