Test point in element

Introduces extension of the Element-interface by adding a method ```bool isPntInElement(GeoLib::Point const& pnt)``` that will return true if the point is located either inside or on the boundary of the element and false otherwise.
For line-elements it tests if the point is located on that line, for 2D elements the point needs to be coplanar with the element nodes and located inside the 2D element.

This introduces a little redundancy to the current Face-interface (i.e. Tri's and Quad's) where already a method ```isPntInside(pnt, eps)``` exists which basically does the same but allows to specify an additional epsilon. Currently, I have left this method as it is. Should I remove it?
no, this is just a test if the tet is coplanar and DN suggested to test vor epsilon instead of "0".
the variable ```eps``` signifies how much p is allowed to be located outside of the tet and still be counted as "inside" (basically to handle numerical errors)