* Added new error calculation
* Refactored large portion of code
Few updates
Merge branch 'dev' of http://github.com/kudkudak/Growing-Neural-Gas into dev

Conflicts:
	inst/include/gng/GNGAlgorithm.h
	inst/include/gng/GNGGraph.h
	inst/include/gng/GNGServer.h
	src/gng/GNGAlgorithm.cpp
	tests/cpp/gng/basic_integration_tests.cpp