Implemented export of 2D meshes as SHPT_POLYGON shapefiles
Made functionality for exporting 2D meshes to Shapefiles available in GUI
removed test functionality from mainwindow and re-inserted previous fix by LB
show error message in gui if shape export failed
Merge pull request #159 from rinkk/Mesh2ShapeExport

Mesh2 shape export
Added logog messages to EarClippingTriangulation::initLists().
Handle special case of 3 collinear vertices in ear clipping algorithm.
Reformating in EarClippingTriangulation::initVertexList().
Return nullptr if surface does not consist of any triangles.
Handle the case the surface (triangulated polygon) is a nullptr.
Removed code that outputs triangulation info.
added shapelib if-defs to keep shapelib optional
Merge pull request #160 from TomFischer/FixTriangulationBug

Fix triangulation bug
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
optimised buiding the mshmodel tree when loading a new mesh
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.
Some small optimisation on GeoTreeModel and StationTreeModel