[MathLib] Tool for testing GaussAlgorithm.

This tool reads a matrix, and solves a simple system of linear equation.
[MathLib] Fix a critical bug in GaussAlgorithm.

Reza discovered a bug within the gauss elimination.
[MathLib] DenseMatrix::write() print the matrix dims, too.
Merge pull request #419 from TomFischer/DenseMatrixReader

Bug fix for gauss algorithm
[FileIO] Implemented getMeshDensityAtStations().
[FileIO] Using station mesh density at station points.
[GMSHPolygonTree] Removed method declarations with missing implementation.
[GMSH] Made docu more specific.
Substituted size_t with std::size_t.
[GMSHPolygonTree] Reduced indentation in insertPolyline().
[PointVec] Documented private method uniqueInsert().
[GMSH] Moved inserting the Polyline to the end of the method.

Before inserting the new polyline, there should be some tests performed with the already existing polylines.
[GMSH] Reformating for readability.
[GMSH] Added GMSHPolygonTree::checkIntersectionsSegmentExistingPolylines().
[GMSH] Included AnalyticalGeometry.h into GMSHPolygonTree.
[FileIO] GMSHInterface::writeGMSHInputFile() Copy stations.
[FileIO::GMSHInterface] More specific debug output.
[FileIO::GMSHInterface] Early exit in case merge_plys does not exist.
[FileIO/GMSHInterface] Compute/add all intersec. pnts between plys.
[GeoLib::PolygonWithSegmentMarker] Definition and impl.

Used in GMSH interface.