Corrected contour generation

[Havrevoll]

The for loop did only read one contour at each level, but often, (also in the example shown), there are several contours on each level, so the program must iterate over all contours and create a dictionary of polygons for each wind speed.

[ecomodeller]

@Havrevoll when changes are complete, (maybe already) just ask for a review

[ecomodeller]

Great.
With this change we combine two arrays and looping over two arrays at the same time can be done with the zip() function.

E.g.:

for collection, level in zip(cn.collections, contour_levels):
    for p in collection.get_paths():
        v = p.vertices
        x = v[:,0]
        y = v[:,1]
        poly = LineString([(i[0], i[1]) for i in zip(x,y)])
        if(poly.is_empty):
            print(f"{i} is empty")
        poly_list.append(dict(wind_speed = level, poly=poly))

I also realized that the GeoDataframe is missing the coordinate reference system.