This data isn't required anymore. The type of
station can be obtained via dynamic_cast.

The type ('simple' station or borehole)
of the object can be obtained by dynamic_cast.

more optimisations, range loops, typos, etc.

The length was used only internaly and
can be computed on the fly. This makes the
cumbersome and errorprone update of the length
unnecessary.

This allows to use MeshLib::Node and GL::Point in
the changed methods.