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 think my answer to your comment went missing ... strange ...
anyway: the method calculates how a plane is oriented in relation to a point (i.e. if the point is left/right or above/below).
to do this it calculates the determinant
d = (a, b, c, d)^T with a = (a_x, a_y, a_z, 1)

so yes, it calculates the determinant *(of a special class)* of 4x4 matrices.