[GeoLib] Describe purpose of file TestGrid.cpp.
Fix memory leaks.
[GeoLib::Grid] Shorten lines -> code more readable.
[GeoLib::Grid] Using std::array instead of "C" array.
Remove two warnings
[GeoLib::Grid] Rewrote initialization of grid data structures.
[MeshLib] Fix warning in test.
[GeoLib::Grid] Test for case x==const.
[GeoLib::Grid] Refactored initNumberOfSteps().
Merge pull request #406 from TomFischer/FixGridMistakes

Fix programming mistakes and compiler warnings concerning class Grid
Remove RapidVtuInterface.h.cpp
Merge pull request #407 from wenqing/rm_warning

Merged PR "Remove two warnings" although there was a failing test. But @rinkk and I did not see a relation between the failing test and the changes done from @wenqing.
[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().