implemented mesh to geometry conversion
mesh to geo conversion is available from gui
moved mesh2geo conversion to MeshLib and removed GMSH2GeoIOclass after discussion with TF
fixed data types and references based upon comments in the pull request
Merge pull request #162 from rinkk/Mesh2GeoConversion

Most points in discussion are a matter of programming style (using for_each or for loops, using or not using lambdas). In my opinion there is not a design error and for this reason I merge the pull request.