[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().