Setting the material group id from a property vector from MeshLib::Mesh.

Until now the material id was set directly in the MeshLib::Element.
Use the property vecs instead of using the val of the elem for material.
Added GocadSGridReader programme to CMakeLists.txt
Added '#include <string>'.
Used MeshLib::Node instead of double coordinates.
Initial commit for GocadSGridReader.
Small changes for compilation with OGS-6.
Added simple program to convert OGS meshes into vtk format.
Removed tool ConvertGliToVtk.
Added namespace qualifier MathLib and including Vector3.h.
Added three methods to class GocadSGridReader.

Added getElements() (public), readElementPropertiesBinary() and createElements() (private).
Added a vector for the created mesh elements.
Corrected a bug in operator() of private class IndexCalculator.
Added logog to GocadSGridReaderMain.cpp and using new functionality of class GocadSGridReader.
Added logog output.
Using logog logging in GocadSGridReader.
Read split nodes and integrate them in elements.

Read split nodes from sg file and change nodes in elements according to the split information.
Fixed a bug inn the case materials can't be read.
Correct typo.
In vtu export write floats with maximum precision to ascii stream.
Throw a runtime_error when reading points was unsuccessful.
Rewrite readNodesBinary() with new readFloat().

Also added new swapFloat() to swap float's bytes.
Some more checks on input stream and results.