implemented GoldStandardCostFunction to prefer correct merges and avoid false merges
made StructuredProblemWriter write gold standard objective
made Segment, Segments, and Slice DiscreteVolumes, propagate resolutions and bounding boxes
checkin of NeuronsMeshExtractor, to get a mesh from a set of neurons
updated gui, imageprocessing, util
added support to select neurons in NeuronsStackView
replaced result 3D view with meshes of selection
Merge remote-tracking branch 'origin/master' into direct_gold_standard

Conflicts:
	binaries/sopnet.cpp
	modules/imageprocessing
	sopnet/sopnet/Sopnet.cpp
	sopnet/sopnet/neurons/NeuronExtractor.cpp
	sopnet/sopnet/segments/Segment.cpp
	sopnet/sopnet/segments/Segment.h
	sopnet/sopnet/slices/Slice.cpp
	sopnet/sopnet/slices/Slice.h
	sopnet/sopnet/training/GoldStandardCostFunction.cpp
	sopnet/sopnet/training/GoldStandardCostFunction.h
	sopnet/sopnet/training/io/StructuredProblemWriter.cpp
	sopnet/sopnet/training/io/StructuredProblemWriter.h
fixed compile errors due to last merge