Make target to generate documentation using doxygen
Use platform-dependent gmsh library name
Use platform specific paths to detect vtk headers and libs
By default build only gcm3d binary
Reworked Node and CalcNode classes
API to set/get values of custom flags in CalcNode
Merge branch 'master' into refactoring

Conflicts:
	src/libgcm/mesh/tetr/TetrMeshSecondOrder.cpp