checks for curl init failure
cycle detection with dijkstra's algorithm
- missing simple tracing changes
- removed scale from load and save nml (it is stored in the config file)
- Tidied up nodeID
reintroduce saving of scale, as it’s used during analysis of skeletons
Merge branch 'master' into segmentation

Conflicts:
	eventmodel.cpp
	skeletonizer.cpp
	skeletonizer.h
	viewer.cpp
	widgets/mainwindow.cpp
	widgets/mainwindow.h
	widgets/tools/toolstreeviewtab.h