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?
I only added this to the derived classes. as far as I know it has no effect in the base class and would need to be implemented in the other classes anyway, so I might just as well not write it here.