GitLab

Introducing IvusTcSliceExtractor processor using Predicate Histogram Widget for classification setup.
So far just a draft - it is working but the results are not really beautiful.

* Slight changes to the API: renamed signal::trigger() to signal::triggerSignal() and signal::queue() to signal::queueSignal()
* Replaced all sigslot signal emits through operator() with emits through emitSignal() to enable debug feature.
* Fixed a possible race condition when deleting a GeometryTransferFunction and its editor window at the same time (as this will happen from different threads).

refs #384

Added implementation for IEEE SciVis 14 submission on "Predicate-based Focus-and-Context Visualization for 3D Ultrasound" (Schulte zu Berge et al.) to advancedusvis module:
* Introducing AbstractPointPredicate base for point predicates and various derived classes
* Introducing PointPredicateHistogram, its corresponding PointPredicateHistogramProperty and the PointPredicateHistogramPropertyWidget
* Introducing PointPredicateEvaluator, PointPredicateRaycaster, PointPredicateVolumeExplorer and ScanlineDistributionComputation processors
* Added demo/reference pipeline implementations for the four data sets from the paper: Achilles tendon, shoulder and two carotid arteries