This function loads wires from previously saved NEC files. Note that,
as wires are loaded rather than elements, the discretisation procedure will
not refine meshes loaded in this fashion. The number of segments on each wire
is loaded from the file, but this will change if the segment length is
changed. The code will only react on GW (including a GC card if
the wire is tapered), GX and GS cards, but will warn the user if
it encounters other control cards in the geometry section of the NEC
file.