Rename Arctic transects tag and flip OSNAP sections

[milenaveneziani]

This does two things:

1. renames the arctic_sections tag to arctic_transport_sections to make it consistent with standard_transport_sections, and also as a reminder that the associated geometric features are mostly used for integrated transport calculations;
2. flips the OSNAP sections to follow the east-to-west direction that is necessary for the positive-northward transport convention in the Northern Hemisphere.

[milenaveneziani]

@xylar: I added the script that I used for doing this. There are some small formatting changes (in the affected geojson features). Please take a look and see if they are ok. Thanks.

[xylar]

Looks good to me. I think we should test it in MPAS-Analysis, though, before we merge.

[xylar]

@milenaveneziani, we probably need to add an aggregator like this one:
https://github.com/MPAS-Dev/geometric_features/blob/master/geometric_features/aggregation/ocean/transport_transects.py
and a section like this one:
https://github.com/MPAS-Dev/geometric_features/blob/master/geometric_features/aggregation/__init__.py#L59-L61
for the Arctic Transport Transects.

Do you want to include that in this PR, too?

[xylar]

This looks good to me. I'd like to make sure it works well with MPAS-Dev/MPAS-Analysis#910 at least and maybe other MPAS-Analysis branches before we merge.