* 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